On the Effect of the Pressure of the Atmosphere on the Mean Level of the Ocean

XII. On the Effect of the Pressure of the Atmosphere on the Mean Level of the Ocean. By Captain Sir James Clark Ross, R.N., D.C.L., F.R.S. &c. Received June 15,—Read June 15, 1854. In September 1848 Her Majesty's ships Enterprize and Investigator entered the harbour of Port Leopold, in latitude 74° N. and longitude 91° W., for the purpose of establishing there a depot of provisions, and of extending, in boats, the examination of the north, south, and west coasts of North Somerset, in search of the missing expedition under the command of Sir John Franklin. No sooner, however, were the ships anchored, than a heavy pack of ice was driven down upon, and completely closed the harbour's mouth, and this effectually preventing their egress, they were compelled there to pass the winter of 1848–49. It was during that period that the series of observations, which I have now the honour of submitting to the consideration of the Royal Society, on the effect of the pressure of the atmosphere on the level of the ocean, was obtained, and as it was made under peculiarly favourable circumstances, which I shall presently point out, I have no doubt it will contribute to throw some light on the movements of the tides, and on some of the causes of their apparent irregularities, not only in the Polar regions, but also along our own coasts, which have not hitherto been detected, or have not received that attention their importance demands. It originated in the following circumstances:—Soon after the harbour had been completely frozen over, a very heavy pressure from the main pack forced the newly-formed sheet of ice, which covered the bay, far up towards its head, carrying the ships with it into such shallow water that at low spring-tides their keels sometimes rested on the ground. It is well known that from many causes great differences in the rise or fall of the tides occur in nearly all latitudes, and as any extraordinary depression, in our case, might seriously injure the ships with so great a weight of ice attached to their sides, the movements of the tides necessarily became to me an object of great anxiety and of careful observation, in order, if possible, to ascertain the amount of irregularities to which they were liable in this particular locality, and to investigate the cause. The first few days' observations evidenced much larger differences in the elevation or depression of successive high or low waters than could be accounted for by any of the generally received causes of disturbance; and I was at once led to connect them with the changes of pressure of the atmosphere, from perceiving that high water was not so high, and that low water was lower, on the days that the pressure of the atmosphere was greater, and that high water was too high, and low water not so low as it ought to have been, on the days of smaller atmospheric pressure. The observations during September and October were limited to the register of high and low water, but various causes of disturbance so frequently masked the effects of the pressure of the atmosphere, that the four observations on each day were not sufficient to determine the amount of effect of its variations: and also, owing to the semidiurnal inequality and other causes of derangement, the usual mode of determining the level, by taking the mean between successive high and low waters, was found inadequate to the detection of small quantities arising from variation of pressure. I therefore adopted a different system of observation from any that has heretofore been practised, in order to determine the mean level of the ocean on each day. I began by instituting simultaneous observations of the height of the tide and of the mercury in the barometer at every quarter of an hour throughout the day and night, and from these I found that the mean level of the ocean for each day could be determined with a great degree of accuracy, and that the variation in the daily mean level and in the mean pressure of the atmosphere, as indicated by the barometer, followed each other in a very remarkable manner, but in an inverse ratio, which could only be accurately obtained by a much more extended series of observations. But the fatigue of making a long-continued series of observations of this nature, at every quarter of an hour, during the inclemency of an arctic winter, was greater than I could expect the officers to endure who had thenceforward to continue the observations which I had begun. Hourly observations were at length determined on. Those which I had previously made having been several times interrupted by the necessity of moving the ships into deeper water, could not be brought into strict comparison with each other without such a complication of corrections to be applied to each set as would have greatly and uselessly extended this communication; they have, therefore, not been employed, and the conclusions which have been arrived at are entirely derived from the observations contained in the following tables. The peculiar advantages of our position at Port Leopold, to which I have before alluded, for making tidal observations were,— 1st. In the great width of the entrance of the harbour admitting the free ingress and egress of the waters, combined with the large field of ice which covered the whole extent of the bay, containing more than ten square miles of surface, and completely subduing those undulations of the water, which in other places render tidal observations uncertain. 2nd. In the steady movement of this immense platform of ice, rising and falling with such singular regularity and precision as to admit the reading off the marks of the tide-pole with the greatest exactness, even to the tenth of an inch; although such minuteness was not always attempted, the nearest quarter of an inch being generally deemed sufficient. 3rd. The shallowness of the water, and the evenness and solidity of the clay bottom admitting the fixture of the tide-pole with immovable firmness. 4th. The whole surface of the ocean in the neighbourhood being, for the greater part of the time, covered by a sheet of ice, preventing those irregularities which occur in other localities from the violence of the wind raising or depressing the ocean in as many different degrees as it varies either in strength or direction. The ships were not finally placed in their winter position until the middle of October, when the operation of fixing the tide-pole engaged our first attention. A hole, 2 feet square, was cut through the icy platform, a strong pole, nearly 40 feet long, passed through it, and driven firmly down several feet into the clay, and fixed by heavy iron weights, which also rested on the clay and prevented any movement of the pole. It was placed in about 21 feet depth of water at the time of mean level of the sea, and by the end of the month was considered, and afterwards proved to have been so perfectly immoveable, that we began the regular series of observations on the 1st of November. Another tide-pole was in like manner fixed through a hole in the ice close to the Investigator, for the sake of reference and comparison. Hourly observations of the tide and the barometer were made by the officers and petty officers of that ship, exactly corresponding with those made by the officers of the Enterprize, throughout the whole of the nine following months, to the end of July, and they proved of great value in many instances, where very large and apparently unaccountable irregularities of the tides occurred, and which otherwise might have been attributed to inaccuracy of observation, or of registry, or of the shifting of the tide-pole, had they not also been observed in every case, at exactly the same time and precisely to the same amount at both the tide-poles. The reduction of the double series of observations, however, would have so greatly increased the labour of preparing this paper as well as its length, that the Investigator's observations have, for the present, been only used for comparison in several cases of uncertainty above alluded to, and for the purpose of refixing the tide-pole of the Enterprize when it was lifted by the ice on the 18th of December. But the whole of the observations of both the ships are preserved in the proper office at the Admiralty, and may at any time be referred to for any purposes of further investigation. The hourly observations which were commenced on the 1st of November, were continued uninterruptedly until the morning of the 18th of December, when the tide-pole having been frozen to the underpart of the ice was drawn out of the ground as the tide rose, and thus made the first break in the series, after forty-seven complete days. The amount of displacement of the pole was easily determined by comparison with that of the Investigator, but several days elapsed before it could be satisfactorily fixed at the same point in which it originally stood. Subsequent observations serve to show that from this time to the middle of July there was a progressive elevation of the mean level of the ocean, and, although of small amount, the difference from month to month was sufficiently evident to render subdivisions of the series desirable, in order that the individual observations of each separate division should be strictly comparable with the others; so that this early interruption is the less to be regretted. The method of observation was as follows:—At the exact hour of mean time the heights of the tide and of the mercury in the barometer were taken; the former by the quarter-master, and the latter by the officer of the watch, who immediately entered both the observations in the meteorological journal, from which the following tables were constructed. Table I.—Showing the height of the sea, and the corresponding height of the mercury in the barometer, for every hour, during the month of November 1848, at Port Leopold. | Hour | November 1. | November 2. | November 3. | November 4. | November 5. | November 6. | |------|-------------|-------------|-------------|-------------|-------------|-------------| | | Tide. Barom.| Tide. Barom.| Tide. Barom.| Tide. Barom.| Tide. Barom.| Tide. Barom. | | A.M. | ft. in. | inches. | ft. in. | inches. | ft. in. | inches. | | 1 | 21 11·5 | 30-122 | 21 3·0 | 30-034 | 21 7·0 | 29-355 | | 2 | 22 2·0 | 30-122 | 21 9·0 | 30-017 | 22 1·0 | 29-356 | | 3 | 21 8·5 | 30-127 | 21 10·0 | 30-000 | 22 5·0 | 29-350 | | 4 | 21 3·5 | 30-132 | 21 6·0 | 29-978 | 22 4·0 | 29-352 | | 5 | 20 1·5 | 30-139 | 20 10·0 | 29-951 | 22 0·0 | 29-318 | | 6 | 19 2·0 | 30-147 | 19 11·0 | 29-926 | 21 6·0 | 29-320 | | 7 | 18 5·5 | 30-142 | 19 2·0 | 29-897 | 20 11·0 | 29-324 | | 8 | 18 2·0 | 30-129 | 18 11·0 | 29-868 | 20 4·5 | 29-342 | | 9 | 18 5·5 | 30-103 | 18 11·5 | 29-833 | 20 1·0 | 29-354 | | 10 | 19 2·2 | 30-100 | 19 6·0 | 29-779 | 20 2·5 | 29-364 | | 11 | 20 4·0 | 30-113 | 20 5·0 | 29-746 | 20 6·0 | 29-362 | | Noon | 21 6·0 | 30-108 | 21 6·0 | 29-683 | 21 1·5 | 29-362 | | 1 | 22 11·0 | 30-110 | 22 7·0 | 29-655 | 22 0·5 | 29-354 | | 2 | 23 6·5 | 30-104 | 23 5·0 | 29-619 | 22 10·0 | 29-356 | | 3 | 23 8·5 | 30-102 | 23 11·0 | 29-609 | 23 5·0 | 29-348 | | 4 | 23 4·0 | 30-092 | 23 11·0 | 29-547 | 23 9·0 | 29-355 | | 5 | 22 6·0 | 30-083 | 23 7·0 | 29-503 | 23 7·5 | 29-353 | | 6 | 21 6·0 | 30-090 | 22 11·0 | 29-452 | 23 2·0 | 29-351 | | 7 | 20 6·5 | 30-080 | 22 1·0 | 29-437 | 22 6·0 | 29-349 | | 8 | 19 8·5 | 30-074 | 21 4·0 | 29-412 | 21 7·0 | 29-350 | | 9 | 19 5·0 | 30-067 | 20 10·5 | 29-385 | 21 3·0 | 29-351 | | 10 | 19 7·0 | 30-056 | 20 8·0 | 29-375 | 20 7·0 | 29-364 | | 11 | 19 11·5 | 30-046 | 20 10·5 | 29-346 | 20 4·0 | 29-369 | | Midnight | 20 8·0 | 30-034 | 21 2·0 | 29-356 | 20 5·0 | 29-374 | | Mean... | 20 9·9 | 30-101 | 21 4·4 | 29-683 | 21 8·3 | 29-351 | | Hour | November 7. | November 8. | November 9. | November 10. | November 11. | November 12. | |------|-------------|-------------|-------------|--------------|--------------|--------------| | | Tide. Barom.| Tide. Barom.| Tide. Barom.| Tide. Barom.| Tide. Barom.| Tide. Barom. | | A.M. | ft. in. | inches. | ft. in. | inches. | ft. in. | inches. | | 1 | 19 5·0 | 30-212 | 19 9·5 | 29-934 | 20 6·0 | 29-656 | | 2 | 18 11·5 | 30-215 | 18 11·0 | 29-902 | 19 4·0 | 29-667 | | 3 | 18 10·5 | 30-215 | 18 6·5 | 29-882 | 18 5·0 | 29-675 | | 4 | 19 2·0 | 30-206 | 18 7·0 | 29-843 | 18 1·0 | 29-680 | | 5 | 19 7·5 | 30-185 | 18 11·0 | 29-840 | 18 5·0 | 29-681 | | 6 | 20 8·5 | 30-182 | 20 2·0 | 29-809 | 19 1·5 | 29-683 | | 7 | 21 3·5 | 30-177 | 21 4·0 | 29-782 | 19 5·5 | 29-686 | | 8 | 21 9·0 | 30-167 | 22 2·0 | 29-770 | 21 9·5 | 29-683 | | 9 | 21 10·5 | 30-162 | 22 10·5 | 29-745 | 23 2·0 | 29-675 | | 10 | 21 7·5 | 30-161 | 22 11·5 | 29-723 | 23 8·5 | 29-683 | | 11 | 21 1·5 | 30-159 | 22 7·5 | 29-718 | 23 9·0 | 29-694 | | Noon | 20 6·0 | 30-136 | 22 1·0 | 29-718 | 23 1·5 | 29-694 | | 1 | 19 9·5 | 30-114 | 20 11·0 | 29-711 | 22 0·5 | 29-707 | | 2 | 19 4·5 | 30-132 | 19 11·7 | 29-721 | 20 10·0 | 29-723 | | 3 | 19 5·5 | 30-112 | 19 4·3 | 29-719 | 19 9·0 | 29-703 | | 4 | 19 9·0 | 30-114 | 19 4·9 | 29-721 | 19 2·5 | 29-745 | | 5 | 20 6·0 | 30-094 | 19 7·5 | 29-737 | 19 3·5 | 29-750 | | 6 | 21 3·5 | 30-066 | 20 9·0 | 29-740 | 19 6·0 | 29-746 | | 7 | 22 1·0 | 30-087 | 21 8·0 | 29-725 | 20 3·5 | 29-744 | | 8 | 22 8·5 | 30-057 | 22 7·0 | 29-717 | 21 10·0 | 29-755 | | 9 | 22 10·5 | 30-010 | 23 3·0 | 29-303 | 23 1·0 | 29-729 | | 10 | 22 11·5 | 30-001 | 23 6·5 | 29-671 | 23 6·0 | 29-734 | | 11 | 21 11·0 | 29-963 | 22 11·5 | 29-655 | 23 7·5 | 29-744 | | Midnight | 20 10·5 | 29-963 | 22 0·0 | 29-661 | 22 9·0 | 29-750 | | Mean... | 20 9·2 | 30-123 | 21 0·4 | 29-756 | 21 0·4 | 29-706 | ### Table I.—November 1848. (Continued.) | Hour | November 13 | November 14 | November 15 | November 16 | November 17 | November 18 | |------|-------------|-------------|-------------|-------------|-------------|-------------| | | Tide. Barom.| Tide. Barom.| Tide. Barom.| Tide. Barom.| Tide. Barom.| Tide. Barom.| | A.M. | ft. in. inches | ft. in. inches | ft. in. inches | ft. in. inches | ft. in. inches | ft. in. inches | | 1 | 22 10-0 30-277 | 23 2-0 30-090 | 22 5-5 30-058 | 21 2-0 30-105 | 20 3-0 29-840 | 20 0-0 29-697 | | 2 | 22 1-0 30-287 | 23 2-0 30-079 | 22 11-0 30-076 | 21 11-5 30-098 | 21 1-0 29-817 | 20 5-0 29-699 | | 3 | 20 10-0 30-290 | 22 4-0 30-058 | 22 8-5 30-081 | 22 3-2 30-081 | 21 7-0 29-813 | 20 9-5 29-704 | | 4 | 19 7-0 30-298 | 20 11-0 30-063 | 21 10-0 30-095 | 22 0-0 30-069 | 21 9-5 29-795 | 21 5-0 29-714 | | 5 | 17 7-0 30-297 | 19 5-0 30-042 | 20 7-0 30-135 | 21 4-0 30-062 | 21 8-5 29-765 | 21 8-0 29-719 | | 6 | 16 8-0 30-299 | 18 4-0 30-060 | 19 3-5 30-155 | 20 3-0 30-043 | 21 1-5 29-749 | 21 9-0 29-719 | | 7 | 16 6-0 30-299 | 17 3-0 30-024 | 18 3-0 30-188 | 19 2-0 30-026 | 20 7-0 29-742 | 21 6-5 29-725 | | 8 | 17 1-5 30-294 | 17 4-0 30-017 | 17 7-5 30-208 | 18 6-0 29-997 | 19 5-0 29-741 | 20 11-0 29-727 | | 9 | 18 8-5 30-292 | 18 2-0 30-025 | 17 11-0 30-226 | 18 3-0 29-985 | 19 1-0 29-727 | 20 3-5 29-753 | | 10 | 20 6-0 30-289 | 19 7-5 30-029 | 19 1-0 30-245 | 18 8-5 29-971 | 19 0-0 29-705 | 19 8-0 29-759 | | Noon | 22 4-5 30-279 | 21 6-0 30-035 | 20 9-0 30-250 | 19 7-5 29-956 | 19 3-5 29-713 | 19 6-5 29-779 | | 1 | 24 0-5 30-277 | 23 3-0 30-028 | 21 5-0 30-246 | 20 11-0 29-942 | 19 11-5 29-701 | 19 8-0 29-789 | | 2 | 24 9-2 30-239 | 24 8-0 30-039 | 23 6-0 30-254 | 22 5-5 29-935 | 21 3-5 29-705 | 20 3-5 29-802 | | 3 | 24 9-0 30-221 | 25 0-5 30-052 | 24 6-0 30-260 | 23 9-0 29-931 | 22 3-5 29-705 | 20 10-5 29-808 | | Midnight | 23 9-0 30-188 | 24 8-0 30-056 | 24 8-5 30-258 | 24 3-5 29-906 | 25 2-5 29-705 | 21 9-5 29-804 | | | Mean ... | 20 6-4 30-225 | 20 11-2 30-047 | 20 10-7 30-185 | 21 1-0 29-957 | 21 2-1 29-727 | 21 1-2 29-780 | | Hour | November 19 | November 20 | November 21 | November 22 | November 23 | November 24 | |------|-------------|-------------|-------------|-------------|-------------|-------------| | | Tide. Barom.| Tide. Barom.| Tide. Barom.| Tide. Barom.| Tide. Barom.| Tide. Barom.| | A.M. | ft. in. inches | ft. in. inches | ft. in. inches | ft. in. inches | ft. in. inches | ft. in. inches | | 1 | 19 1-0 29-858 | 19 4-5 29-679 | 19 8-0 29-771 | 19 10-0 29-924 | 20 6-0 29-961 | 21 2-5 29-901 | | 2 | 19 4-0 29-850 | 19 2-5 29-677 | 18 11-0 29-790 | 18 11-0 29-929 | 19 7-0 29-949 | 20 1-0 29-903 | | 3 | 19 10-0 29-847 | 19 5-5 29-671 | 18 9-5 29-797 | 18 6-0 29-931 | 18 7-0 29-954 | 19 0-5 29-908 | | 4 | 20 6-0 29-830 | 19 10-0 29-651 | 19 0-5 29-790 | 18 5-0 29-937 | 18 3-0 29-957 | 18 6-0 29-909 | | 5 | 21 1-0 29-822 | 20 6-0 29-652 | 19 8-0 29-799 | 18 11-0 29-934 | 18 7-0 29-962 | 18 0-5 29-919 | | 6 | 21 5-5 29-819 | 21 2-0 29-656 | 20 6-0 29-804 | 19 9-0 29-929 | 19 8-0 29-955 | 18 9-5 29-910 | | 7 | 21 6-0 29-800 | 21 10-0 29-663 | 21 4-5 29-808 | 20 9-0 29-932 | 20 6-0 29-957 | 19 9-0 29-900 | | 8 | 21 5-0 29-798 | 22 2-0 29-679 | 22 0-0 29-815 | 21 10-5 29-924 | 21 8-0 29-957 | 20 11-0 29-898 | | 9 | 21 1-0 29-774 | 22 0-0 29-687 | 22 9-0 29-811 | 22 7-0 29-929 | 22 9-5 29-957 | 22 5-0 29-889 | | 10 | 20 7-5 29-760 | 21 8-0 29-696 | 22 3-0 29-816 | 22 10-0 29-937 | 23 5-0 29-962 | 23 5-5 29-879 | | Noon | 20 2-0 29-757 | 21 1-0 29-696 | 21 10-0 29-822 | 22 7-0 29-937 | 23 6-0 29-952 | 23 11-5 29-870 | | 1 | 19 11-2 29-738 | 20 3-0 29-712 | 21 1-5 29-831 | 22 0-5 29-929 | 23 1-0 29-934 | 23 9-2 29-880 | | 2 | 19 11-5 29-748 | 20 0-5 29-712 | 20 5-5 29-835 | 21 1-5 29-935 | 22 2-0 29-920 | 22 6-0 29-891 | | 3 | 20 3-0 29-766 | 19 11-0 29-712 | 19 8-5 29-861 | 20 2-5 29-937 | 21 2-0 29-922 | 21 11-5 29-897 | | Midnight | 20 11-0 29-751 | 20 1-0 29-717 | 19 6-5 29-875 | 19 6-5 29-953 | 20 1-0 29-927 | 20 7-0 29-896 | | | Mean ... | 21 7-0 29-700 | 20 7-0 29-717 | 19 9-0 29-881 | 19 4-0 29-951 | 19 5-5 29-922 | 20 3-0 29-880 | | 4 | 22 5-0 29-664 | 22 7-5 29-740 | 22 6-0 29-896 | 22 3-5 30-034 | 22 1-0 29-922 | 21 9-0 29-894 | | 5 | 22 3-5 29-664 | 22 4-0 29-737 | 22 3-5 29-896 | 22 7-0 30-084 | 22 8-0 29-908 | 22 7-0 29-892 | | 6 | 22 9-0 29-699 | 21 11-5 29-725 | 21 0-0 29-899 | 20 2-0 29-943 | 19 8-0 29-936 | 19 3-5 29-888 | | 7 | 23 0-5 29-700 | 22 8-0 29-723 | 21 9-0 29-903 | 21 1-0 29-945 | 20 6-0 29-930 | 19 9-0 29-898 | | 8 | 22 10-0 29-682 | 22 11-0 29-730 | 22 2-5 29-903 | 21 10-5 29-948 | 21 4-0 29-930 | 20 9-0 29-897 | | 9 | 22 5-0 29-664 | 22 7-5 29-740 | 22 6-0 29-896 | 22 3-5 30-034 | 22 1-0 29-922 | 21 9-0 29-894 | | 10 | 21 8-5 29-664 | 22 4-0 29-737 | 22 3-5 29-896 | 22 7-0 30-084 | 22 8-0 29-908 | 22 7-0 29-892 | | 11 | 20 8-0 29-669 | 21 6-5 29-751 | 21 9-0 29-838 | 22 3-5 30-128 | 22 9-0 29-902 | 22 10-5 29-901 | | Midnight | 20 0-0 29-669 | 20 7-5 29-777 | 20 11-0 29-913 | 21 7-0 30-066 | 22 2-0 29-898 | 22 10-0 29-908 | | | Mean ... | 21 0-2 29-753 | 21 0-5 29-703 | 20 9-8 29-847 | 21 2-3 29-953 | 20 11-2 29-937 | 21 0-2 29-896 | MDCCCLIV. ### Table I.—November 1848. (Continued.) | Hour | November 25. | November 26. | November 27. | November 28. | November 29. | November 30. | |------|--------------|--------------|--------------|--------------|--------------|--------------| | A.M. | ft. in. inches | ft. in. inches | ft. in. inches | ft. in. inches | ft. in. inches | ft. in. inches | | 1 | 21 9-5 29-908 | 22 1-0 29-920 | 22 6-0 29-861 | 22 4-5 29-822 | 22 4-0 29-791 | 22 1-0 29-840 | | 2 | 20 8-0 29-914 | 21 2-0 29-940 | 21 8-0 29-853 | 21 11-0 29-821 | 22 3-5 29-706 | 22 2-5 29-854 | | 3 | 19 7-0 29-889 | 20 1-0 29-946 | 20 6-0 29-849 | 20 11-0 29-799 | 21 6-5 29-708 | 21 10-0 29-854 | | 4 | 18 7-0 29-891 | 19 0-0 29-944 | 19 5-0 29-847 | 19 10-0 29-791 | 20 9-0 29-712 | 21 2-5 29-856 | | 5 | 18 2-0 29-886 | 18 3-0 30-025 | 18 5-0 29-858 | 18 8-0 29-819 | 19 7-5 29-717 | 20 1-5 29-863 | | 6 | 18 1-5 29-868 | 18 1-0 30-052 | 18 1-0 29-847 | 18 2-0 29-821 | 18 9-0 29-719 | 19 1-0 29-866 | | 7 | 19 1-0 29-872 | 18 8-0 30-033 | 18 3-0 29-836 | 17 11-5 29-821 | 18 3-0 29-693 | 18 7-0 29-862 | | 8 | 20 3-5 29-874 | 20 5-0 30-006 | 19 1-0 29-830 | 18 5-5 29-821 | 18 5-0 29-691 | 18 4-5 29-869 | | 9 | 21 4-5 29-875 | 21 3-5 29-939 | 20 7-0 29-827 | 19 9-0 29-823 | 19 4-5 29-681 | 18 11-5 29-874 | | 10 | 23 3-0 29-862 | 22 1-0 29-933 | 22 1-5 29-823 | 21 4-0 29-814 | 20 8-0 29-685 | 20 1-0 29-887 | | Noon | 24 2-0 29-858 | 24 0-5 29-931 | 23 3-5 29-822 | 22 7-0 29-789 | 21 10-5 29-684 | 21 3-0 29-901 | | 1 | 24 4-5 29-878 | 24 7-0 29-919 | 24 3-0 29-785 | 23 9-0 29-775 | 23 5-0 29-708 | 22 6-0 29-910 | | 2 | 23 10-0 29-865 | 24 5-0 29-917 | 24 5-0 29-785 | 24 4-5 29-763 | 24 4-0 29-720 | 23 9-0 29-913 | | 3 | 22 10-0 29-867 | 23 9-0 29-921 | 23 11-0 29-809 | 24 4-0 29-754 | 24 6-5 29-730 | 24 2-5 29-906 | | Midnight | 21 7-5 29-871 | 22 6-5 29-924 | 23 0-0 29-808 | 23 5-0 29-755 | 24 1-5 29-723 | 24 2-5 29-912 | | Mean ... | 21 0-0 29-889 | 21 1-3 29-936 | 21 0-5 29-830 | 20 11-6 29-773 | 21 1-5 29-733 | 21 1-1 29-903 | ### December 1848. | Hour | December 1. | December 2. | December 3. | December 4. | December 5. | December 6. | |------|-------------|-------------|-------------|-------------|-------------|-------------| | A.M. | ft. in. inches | ft. in. inches | ft. in. inches | ft. in. inches | ft. in. inches | ft. in. inches | | 1 | 21 7-0 29-959 | 20 11-5 29-919 | 20 3-5 29-983 | 19 10-0 29-886 | 19 0-5 29-815 | 18 10-0 29-835 | | 2 | 21 11-2 29-966 | 21 7-0 29-930 | 21 0-0 29-971 | 20 3-5 29-859 | 19 4-5 29-811 | 18 7-5 29-860 | | 3 | 21 11-0 29-978 | 21 11-0 29-932 | 21 6-0 29-967 | 20 11-0 29-864 | 19 10-5 29-810 | 18 10-0 29-877 | | 4 | 21 6-0 29-980 | 21 9-0 29-938 | 21 10-0 29-946 | 21 6-0 29-865 | 20 6-0 29-803 | 19 6-0 29-896 | | 5 | 20 9-0 29-997 | 21 2-0 29-934 | 21 9-0 29-938 | 20 8-0 29-867 | 21 0-0 29-808 | 20 3-0 29-939 | | 6 | 19 11-0 30-002 | 20 7-5 29-947 | 21 4-5 29-935 | 21 10-0 29-869 | 21 5-5 29-797 | 21 1-0 29-943 | | 7 | 19 1-0 30-000 | 19 10-0 29-961 | 20 9-5 29-941 | 20 8-5 29-876 | 21 7-0 29-799 | 21 9-0 29-964 | | 8 | 18 8-0 30-162 | 19 2-0 29-975 | 20 2-5 29-935 | 20 10-5 29-864 | 21 6-0 29-784 | 22 0-5 29-962 | | 9 | 18 10-0 29-971 | 19 7-0 29-979 | 19 7-0 29-935 | 20 5-0 29-861 | 21 1-5 29-784 | 21 10-0 29-967 | | 10 | 19 6-0 29-958 | 19 4-0 29-954 | 20 0-0 29-859 | 20 8-0 29-780 | 21 6-0 29-976 | | Noon | 20 6-5 29-957 | 19 10-5 30-002 | 19 6-0 29-954 | 19 10-5 29-846 | 20 3-0 29-772 | 20 9-0 29-995 | | 1 | 21 8-0 29-952 | 20 10-0 30-018 | 20 1-5 29-947 | 20 0-0 29-826 | 19 11-0 29-776 | 20 0-5 30-007 | | 2 | 22 10-5 29-953 | 21 11-5 30-041 | 21 0-5 29-950 | 20 6-0 29-826 | 19 9-5 29-750 | 19 6-0 30-021 | | 3 | 23 9-0 29-953 | 22 10-0 30-041 | 22 0-5 29-950 | 21 3-0 29-830 | 20 0-5 29-758 | 19 3-5 30-039 | | Midnight | 24 1-5 29-950 | 23 6-5 30-049 | 22 9-5 29-949 | 22 0-0 29-822 | 20 9-0 29-773 | 19 8-0 30-045 | | 4 | 23 10-5 29-945 | 23 8-0 30-051 | 23 4-0 29-949 | 22 5-5 29-837 | 21 3-5 29-778 | 20 2-5 30-055 | | 5 | 23 2-5 29-937 | 23 5-5 30-057 | 23 4-0 29-950 | 22 11-5 29-824 | 22 2-0 29-788 | 20 10-5 30-061 | | 6 | 22 5-5 29-914 | 22 9-0 30-053 | 23 1-0 29-939 | 23 2-0 29-824 | 22 8-0 29-789 | 21 8-5 30-079 | | 7 | 21 2-5 29-912 | 21 11-0 30-048 | 22 11-0 29-929 | 22 9-0 29-824 | 22 10-5 29-793 | 22 6-0 30-078 | | 8 | 20 6-5 29-907 | 21 0-0 30-053 | 21 7-0 29-931 | 22 3-0 29-824 | 22 7-5 29-811 | 22 8-5 30-084 | | 9 | 19 9-0 29-902 | 20 2-0 30-068 | 20 9-0 29-911 | 21 5-0 29-826 | 22 0-0 29-799 | 22 5-0 30-097 | | 10 | 19 8-0 29-910 | 19 9-0 30-044 | 19 11-0 29-891 | 20 5-0 29-822 | 21 2-5 29-801 | 21 9-0 30-096 | | 11 | 20 0-5 29-902 | 19 8-0 29-995 | 19 6-0 29-898 | 19 8-5 29-822 | 20 2-5 29-818 | 20 10-0 30-094 | | Midnight | 20 5-0 29-904 | 19 10-0 30-010 | 19 5-0 29-891 | 19 3-0 29-813 | 19 3-5 29-822 | 19 9-0 30-111 | | Mean ... | 21 1-9 29-957 | 21 1-2 30-002 | 21 1-5 29-938 | 21 1-3 29-843 | 20 10-6 29-792 | 20 8-1 30-001 | ## ATMOSPHERE ON THE MEAN LEVEL OF THE OCEAN. ### Table I.—December 1848. (Continued.) | Hour | December 7. | December 8. | December 9. | December 10. | December 11. | December 12. | |------|---------------|----------------|------------------|------------------|-----------------|----------------| | | Tide. Barom. | Tide. Barom. | Tide. Barom. | Tide. Barom. | Tide. Barom. | Tide. Barom. | | A.M. | ft. in. | inches | ft. in. | inches | ft. in. | inches | | 1 | 18 9-0 | 30-122 | 19 4-0 | 30-054 | 20 10-0 | 29-738 | | 2 | 18 2-0 | 30-142 | 18 0-0 | 30-061 | 19 6-0 | 29-743 | | 3 | 18 1-0 | 30-141 | 17 11-0 | 30-056 | 18 4-5 | 29-745 | | 4 | 18 6-0 | 30-151 | 17 11-0 | 30-043 | 17 9-5 | 29-751 | | 5 | 19 4-0 | 30-146 | 18 8-0 | 30-035 | 17 11-0 | 29-753 | | 6 | 20 4-0 | 30-145 | 19 7-5 | 30-032 | 18 8-5 | 29-755 | | 7 | 21 5-0 | 30-147 | 21 0-5 | 30-040 | 20 2-0 | 29-758 | | 8 | 22 3-0 | 30-139 | 22 5-5 | 29-987 | 21 10-0 | 29-755 | | 9 | 22 9-0 | 30-132 | 23 2-5 | 29-966 | 23 6-0 | 29-750 | | 10 | 22 6-0 | 30-132 | 23 11-0 | 29-953 | 24 4-0 | 29-754 | | 11 | 21 11-0 | 30-130 | 23 8-5 | 29-921 | 24 9-0 | 29-751 | | Noon | 21 0-0 | 30-123 | 22 6-5 | 29-911 | 24 3-0 | 29-745 | | 1 | 20 2-0 | 30-124 | 21 10-0 | 29-899 | 23 11-0 | 29-755 | | 2 | 19 5-0 | 30-117 | 20 7-5 | 29-881 | 21 10-0 | 29-768 | | 3 | 19 2-0 | 30-115 | 19 10-0 | 29-856 | 20 6-0 | 29-755 | | 4 | 19 5-0 | 30-115 | 19 5-0 | 29-849 | 19 6-0 | 29-760 | | 5 | 20 0-0 | 30-111 | 19 5-0 | 29-820 | 19 1-0 | 29-781 | | 6 | 20 10-0 | 30-109 | 20 1-0 | 29-814 | 19 3-0 | 29-780 | | 7 | 21 8-5 | 30-108 | 20 11-0 | 29-803 | 19 10-0 | 29-780 | | 8 | 22 3-5 | 30-106 | 22 1-0 | 29-792 | 20 10-5 | 29-793 | | 9 | 22 8-0 | 30-099 | | | 22 2-5 | 29-795 | | 10 | 22 6-0 | 30-095 | | | 23 0-0 | 29-793 | | 11 | 21 8-0 | 30-085 | | | 23 3-5 | 29-805 | | Midnight | | | | | | 22 11-0 | | Mean ... | 20 7-7 | 30-121 | | | | 20 11-0 | | | | | | | | 20 11-6 | | Hour | December 13. | December 14. | December 15. | December 16. | December 17. | December 18. | |------|--------------|--------------|--------------|--------------|--------------|--------------| | | Tide. Barom. | Tide. Barom. | Tide. Barom. | Tide. Barom. | Tide. Barom. | Tide. Barom. | | A.M. | ft. in. | inches | ft. in. | inches | ft. in. | inches | | 1 | 22 11-0 | 29-914 | 22 7-0 | 29-847 | 21 10-5 | 29-736 | | 2 | 22 10-0 | 29-910 | 23 0-5 | 29-833 | 22 7-0 | 29-726 | | 3 | 21 11-0 | 29-915 | 22 9-5 | 29-825 | 22 9-5 | 29-718 | | 4 | 20 7-5 | 29-911 | 21 10-0 | 29-823 | 22 6-5 | 29-721 | | 5 | 19 0-0 | 29-926 | 20 6-5 | 29-805 | 21 7-5 | 29-717 | | 6 | 17 11-0 | 29-925 | 19 4-5 | 29-808 | 20 7-0 | 29-715 | | 7 | 17 8-0 | 29-911 | 18 3-0 | 29-808 | 19 6-0 | 29-710 | | 8 | 17 5-0 | 29-899 | 17 11-0 | 29-808 | 18 10-0 | 29-711 | | 9 | 18 6-0 | 29-894 | 18 5-0 | 29-793 | 18 9-0 | 29-705 | | 10 | 20 3-0 | 29-878 | 19 4-0 | 29-783 | 19 1-0 | 29-710 | | 11 | 22 2-0 | 29-875 | 21 1-0 | 29-776 | 20 1-0 | 29-710 | | Noon | 23 10-5 | 29-875 | 22 9-0 | 29-774 | 21 3-0 | 29-707 | | 1 | 25 1-0 | 29-886 | 24 3-0 | 29-762 | 22 11-0 | 29-657 | | 2 | 25 5-0 | 29-895 | 25 1-0 | 29-823 | 24 1-0 | 29-705 | | 3 | 25 0-0 | 29-878 | 25 1-0 | 29-802 | 24 10-0 | 29-700 | | 4 | 23 11-0 | 29-872 | 24 8-0 | 29-800 | 24 8-0 | 29-692 | | 5 | 22 3-5 | 29-890 | 23 7-0 | 29-784 | 24 2-0 | 29-711 | | 6 | 20 11-0 | 29-899 | 22 6-0 | 29-771 | 23 5-5 | 29-719 | | 7 | 20 3-0 | 29-885 | 20 7-0 | 29-769 | 21 8-0 | 29-731 | | 8 | 18 6-0 | 29-879 | 19 5-5 | 29-758 | 20 3-0 | 29-727 | | 9 | 18 7-0 | 29-863 | 18 9-0 | 29-761 | 19 5-5 | 29-742 | | 10 | 19 1-0 | 29-853 | 19 11-0 | 29-743 | 19 2-0 | 29-740 | | 11 | 20 4-5 | 29-847 | 19 8-0 | 29-739 | 19 5-0 | 29-740 | | Midnight | | | | | | 19 11-0 | | Mean ... | 21 1-0 | 29-887 | 21 3-6 | 29-790 | 21 4-5 | 29-718 | Tide-pole frozen into the ice, and lifted with rising tide above 4 inches. Explanation of Tables A. and B. which follow: From the preceding Tables, the arithmetic mean of the hourly observations of the height of the sea for each day is taken as the mean level of the ocean for that day, and the mean of the hourly observed heights of the barometer as the corresponding mean pressure of the atmosphere; these mean levels, and corresponding mean pressures, are brought together in the following Table A., arranged in the order of the days of observation. In Table B., commencing with the day of greatest mean pressure, they are arranged in the order of the mean heights of the barometer, with the corresponding mean levels, without regard to the dates of observation, for the purpose of showing the dependence the latter have on the former. In the diagram of curves which is formed from Table A., the abscissæ represent the days of the month, from the 1st of November to the end of December 1848; the ordinates in the upper half of the diagram the observed mean level of the ocean, and in the lower half the corresponding mean height of the barometer on each day during that period. ### Table A. | Date. 1848 | Observed level | Observed Barom. | |------------|----------------|-----------------| | Nov. | ft. in. | inches | | | | | | Nov. 1 | 20 9·9 | 30·101 | | | 21 4·4 | 30·683 | | | 21 8·3 | 29·551 | | | 21 3·5 | 29·643 | | | 20 9·7 | 30·108 | | | 20 8·1 | 30·270 | | | 20 9·2 | 30·123 | | | 21 0·4 | 29·756 | | | 21 0·4 | 29·706 | | | 21 0·7 | 29·759 | | | 20 10·0 | 29·894 | | | 20 11·7 | 30·064 | | | 20 6·4 | 29·225 | | | 20 11·2 | 30·047 | | | 20 10·7 | 30·185 | | | 21 1·0 | 29·957 | | | 21 2·1 | 29·727 | | | 21 1·2 | 29·780 | | | 21 0·2 | 29·753 | | | 21 0·5 | 29·703 | | | 20 9·8 | 29·847 | | | 21 2·3 | 29·953 | | | 20 11·2 | 29·937 | | | 21 0·2 | 29·896 | | | 21 0·0 | 29·889 | | | 21 1·3 | 29·936 | | | 21 0·5 | 29·830 | | | 20 11·6 | 29·773 | | | 21 1·5 | 29·733 | | | 21 1·1 | 29·903 | | Dec. | 21 1·9 | 29·957 | | | 21 1·2 | 30·002 | | | 21 1·5 | 29·938 | | | 21 1·3 | 29·843 | | | 20 10·6 | 29·792 | | | 20 8·1 | 30·001 | | | 20 7·7 | 30·121 | | | 20 11·9 | 29·903 | | | 20 11·0 | 29·894 | | | 20 11·6 | 29·887 | | | 20 11·6 | 29·887 | | | 20 11·9 | 29·903 | | | 20 10·6 | 29·766 | | | 20 11·6 | 29·879 | | | 20 11·6 | 29·879 | | | 20 11·6 | 29·879 | | | 20 11·6 | 29·879 | | | 20 11·6 | 29·879 | | | 20 11·6 | 29·879 | | | 20 11·6 | 29·879 | | | 20 11·6 | 29·879 | | | 20 11·6 | 29·879 | | | 20 11·6 | 29·879 | ### Table B. | Date. 1848 | Observed Barom. | Observed level | Corrections | True level | Remarks | |------------|-----------------|----------------|-------------|------------|---------| | Nov. 6 | 30·270 | 20 8·1 | +5·24 | 21 1·34 | inches | | Nov. 13 | 30·285 | 20 9·4 | +4·64 | 20 11·04 | Barom. | | Nov. 15 | 30·185 | 20 10·7 | +4·11 | 21 2·81 | ft. in. | | Nov. 5 | 30·168 | 20 9·7 | | | Level | | Nov. 7 | 30·123 | 20 9·2 | | | Correction| | Dec. 7 | 30·121 | 20 7·7 | Mean ... | | Corrected level...21 1·06 | | Nov. 1 | 30·101 | 20 9·9 | | | | | Nov. 12 | 30·064 | 20 11·7 | | | | | Dec. 17 | 30·052 | 20 10·7 | | | | | Nov. 14 | 30·047 | 20 11·2 | | | | | Dec. 2 | 30·002 | 21 1·2 | | | | | Dec. 6 | 30·001 | 20 8·1 | | | | | Nov. 16 | 29·957 | 21 1·0 | | | | | Dec. 1 | 29·957 | 21 1·9 | | | | | Nov. 22 | 29·953 | 21 2·3 | | | | | Dec. 3 | 29·938 | 21 1·5 | | | | | Nov. 23 | 29·937 | 20 11·2 | | | | | Nov. 26 | 29·936 | 21 1·3 | | | | | Dec. 10 | 29·905 | 20 10·6 | | | | | Nov. 30 | 29·903 | 21 1·1 | | | | | Dec. 8 | 29·903 | 20 11·9 | | | | | Nov. 24 | 29·896 | 21 0·2 | | | | | Nov. 11 | 29·894 | 20 10·0 | | | | | Nov. 25 | 29·889 | 21 0·0 | | | | | Dec. 12 | 29·887 | 20 11·6 | | | | | Dec. 13 | 29·887 | 21 1·0 | | | inches | | Dec. 11 | 29·879 | 20 11·0 | | | Barom. | | Nov. 21 | 29·847 | 20 9·8 | | | ft. in. | | Dec. 4 | 29·843 | 21 1·3 | | | Level | | Dec. 16 | 29·837 | 21 2·4 | | | | | Nov. 27 | 29·830 | 21 0·5 | | | | | Dec. 5 | 29·792 | 20 10·6 | | | | | Dec. 14 | 29·790 | 21 3·6 | | | | | Nov. 18 | 29·780 | 21 1·2 | | | | | Nov. 28 | 29·773 | 20 11·6 | | | | | Dec. 9 | 29·766 | 21 2·0 | | | | | Nov. 10 | 29·759 | 21 0·7 | | | | | Nov. 8 | 29·756 | 21 0·4 | | | | | Nov. 19 | 29·753 | 21 0·2 | | | | | Nov. 29 | 29·733 | 21 1·5 | | | | | Nov. 17 | 29·727 | 21 2·1 | | | inches | | Dec. 15 | 29·718 | 21 4·5 | | | Barom. | | Nov. 9 | 29·706 | 21 0·4 | | | ft. in. | | Nov. 20 | 29·703 | 21 0·5 | | | Level | | Nov. 2 | 29·683 | 21 4·4 | -2·53 | 21 1·67 | Correction| | Nov. 4 | 29·643 | 21 3·5 | -3·05 | 21 0·45 | | | Nov. 3 | 29·551 | 21 8·3 | -7·02 | 21 1·28 | | | Mean ... | 29·874 | 21 0·21 | -6·0 | Corrected level...21 1·23 | | Mean ... | 21 1·2 | | | | | The result of these forty-seven days of hourly observations gives for the mean height of the barometer 29·874 inches, and the mark of the mean level of the ocean 21 feet 0·21 inch. In order to avoid the effects of accidental irregularities, the means of the three days of greatest and of least pressure are taken to compare with the mean level of the ocean on the corresponding days, and from the difference of the pressures and the difference of the levels to determine the relation of each to the other. | inches | ft. in. | |--------|--------| | The mean of three days' greatest pressure was | 30·227 | Of corresponding level | 20 8·4 | | The mean of three days' least pressure was | 29·559 | Of corresponding level | 21 5·4 | | Difference | .668 | Difference | 9·0 | Thus a difference of pressure equal to .668 of an inch in the barometer, produces a difference of 9 inches in the mean level of the ocean, from which we can of course readily compute the exact relation of cause and effect. Thus the difference of level, 9 inches, divided by the difference of pressure 0·668 of an inch, equals 13·467. The effect, therefore, of the pressure of the atmosphere on the level of the ocean is 13·467 times greater than the effect it produces on the mercury in the barometer, or very nearly in the inverse ratio of the specific gravity of the two bodies; that of the sea- water being 1·026, and that of mercury 13·566, or as 1 to 13·224. This remarkable coincidence of the results must, however, in this case be con- sidered in a great measure accidental, for if instead of the three days' greatest and least pressure we were to take seven days of each, from which a better result might be expected, we find, instead of the ratio being as 1 to 13·467, it would by these means become as 1 to 12·562; and if we take the mean of twelve highest and twelve lowest barometers, the ratio would be still further reduced as 1 to 11·60; but these differences in the result are chiefly caused by the evident irregularities of the mean level on the 9th and 20th of November, occasioned by a heavy gale of wind, in each case of two days' continuance. This circumstance, although accounted for in this particular instance, seems to indicate the necessity of multiplying observations of this nature before exact results can be determined. I may here remark, that the effect produced appears from these observations to be strictly uniform in its progression from the greatest to the least pressure. By com- bining the mean of the three days' observations of next greater and three days of less pressure with that nearest to the mean pressure for the whole period, we find the result corresponds nearly with the mean pressure, and the ratio between the ex- tremes almost equal; thus, on December 11, the mean pressure was 29·879, differing very little from the mean of the whole period; and the three days' observations above and below combined with it, give a mean of 29·867, the corresponding mean level of the seven days being 21 ft. 0·16 in., which so closely approaches that of the whole period, that they may be deemed identical, and would tend to show that the effect from the greatest to the mean pressure, and from the mean to the least pressure, is in strict progression. It is not possible, however, from so limited a number of obser- vations, to determine this point with certainty, or to attempt any intermediate infer- ences. We have, from these observations, been able to deduce results which plainly point to the law which governs the effect of the pressure of the atmosphere on the mean level of the ocean, and may be encouraged to pursue the investigation through a more extended series of observations, in order that we may at length arrive at the most accurate conclusion that the observed facts may justify. For all practical purposes, it may in the mean time be well to assume, what the preceding observations seem to indicate, that the ocean is a water barometer on a vast scale of magnificence, and that the level of its surface is disturbed by every variation of atmospheric pressure, inversely as the mercury in the barometer, and exactly in the ratio of the relative specific gravities of the water and the mercury. And as all observations of the tides, before they can be safely employed to investigate the laws by which they are governed, should in the first place be corrected for the large and hitherto mysterious irregularities which the variations in the pressure of the atmosphere produce, the following formula may be used to determine the correction $z$ to be applied to all observations of the height of the tide, or the mean level of the ocean deduced from them, to reduce them to the mean pressure of the atmosphere. \[(1) \ z = (B - \beta)D, \text{ or } (2) \ L = \lambda \pm (B - \beta)D,\] positive when $\beta$ is greater than $B$, and negative when less. In which $B$ denotes the mean pressure of the atmosphere. $L$ the correct height of the tide or mean level of the ocean. $D$ the relative specific gravity of sea-water and mercury. $\lambda$ the observed height of the tide or observed level of the ocean. $\beta$ the corresponding height of the barometer. And if we assume $B = 29.874$ inches, the mean of the preceding observations; $L = 21$ ft. 0.21 inch, the mean of the preceding observations; and $D = 13.224$, we can readily compute the correction $z$ to be applied to any observed tide, having the corresponding height of the barometer. For example, on the 3rd November the mean barometer for the day was $\beta = 29.351$ inches, and the corresponding mean level of the sea $\lambda = 21$ ft. 8.3 inches; then $B - \beta \times D = -6.92$, which applied to $\lambda = 21$ ft. 1.38 inch; and on the 13th November the mean barometer was $\beta = 30.225$ inches, and the corresponding observed level $\lambda = 20$ ft. 6.4 inches; again, $B - \beta \times D = +4.64$ added to $\lambda = 20$ ft. 11.04 inches. On these two days the observed level of the ocean differed no less than 14 inches; but by the application of the correction found by the above formula, the observed level in each day is brought to agree with the true mean level to little more than 1 inch. I may further observe, that much greater irregularities are to be hereafter noticed in the more extensive series of observations which followed this, and by the same formula are capable of being reduced to an equally near accordance with the mean level, as deduced from the whole of the observations. Thus it is evident that one of the many causes of the apparent irregularities of the tides (and at Port Leopold certainly the greatest of all) is clearly traceable to a well-established and invariable law. POSTSCRIPT. When this paper was drawn up some years ago I was ignorant of the researches of M. Daussy on the same subject, or the confirmation of his discovery by Sir John Lubbock, whose valuable treatise on the Tides having been long out of print is, unfortunately, too little known to naval officers. Dr. Whewell directed my attention to it when I mentioned to him the result of my deductions from the observations at Port Leopold, and although the investigations of these eminent philosophers relate only to the effect of the pressure of the atmosphere on the height of high water, and differ widely in their results, owing to the localities in which the observations were made being unfavourable for the detection of the universal law which governs the amount of apparent irregularities, I have extracted from Sir John Lubbock's work a paragraph which clearly shows the exact state of the question previous to my investigations. He says, p. 48, "M. Daussy has ascertained that at Brest the height of the high water varies inversely as the height of the barometer, and that the British Channel there rises more than 8 inches for a fall of about half an inch in the barometer. I have found that at Liverpool a fall of a tenth of an inch in the barometer corresponds to a rise in the River Mersey of about an inch, and that at the London Docks a fall of one-tenth of an inch in the barometer corresponds to a rise in the River Thames of about seven-tenths of an inch. So that with a low barometer the tides may be expected to be high, and vice versa caeteris paribus." Thus M. Daussy found the height of high water to be affected At Brest in the ratio of . . . . . . 1 : 16 Sir John Lubbock at Liverpool . . . 1 : 10 And at London . . . . . . . . . . 1 : 7 The results of their investigations at these three places differed so much from each other, that their practical application became limited to the correction of the height of high water at the places where the observations were made. The result of the deductions from the observations at Port Leopold is, I have no doubt, of more universal application in all harbours where the ocean has free ingress and egress, as a comparison with the extensive series of tidal observations made at New Zealand, Cape Horn and the Falkland Islands, during my voyage to the Antarctic Seas in 1839 to 1843, tends to show. But the subject is well worthy of investigation in other localities, as doubtless a different ratio will be found to obtain in proportion as the ingress of the waters of the ocean is free, or obstructed by narrow channels or sand-banks. J. C. R. Aston-Abbott's House, Aylesbury, November 6, 1854.