An Account of Some Observations, Made This Present Year by Capt. Samuel Sturmy in Hong-Road within Four Miles of Bristol, in Answer to Some of the Queries Concerning the Tydes, in No. 17 & No. 18

PHILOSOPHICAL TRANSACTIONS. Monday, Novemb. 16. 1668. The Contents. An Account from Bristol of some Observations made in Hong-road this present year, by way of Answer to some of the Queries concerning the Tydes, recommended No. 17 & No. 18. An Extract of a Narrative communicated from Sevill, of Observations made in a late Voyage from Spain to Mexico, concerning the Minerals of Mexico, and particularly the exact and perfect way of separating the Silver from its Ore by Mercury, together with divers other Curiosities, Natural and Chymical. Continuation of Dr. Wallis's second Letter on the printed Paper of Franciscus De Laurens. An Account of two Books: I. Tractatus duo, prior de RESPIRATIONE; alter de RACHITIDE, A. F. O. H. MAYOW, &c. Oxon. 1668. in 8°. II. A Discourse concerning PHYSICK, and the many Abuses thereof by APOTHECARIES. London, 1668. in 8°. An Account of some Observations, made this present year by Capt. Samuel Sturmy in Hong-road within four miles of Bristol, in Answer to some of the Queries concerning the Tydes, in No. 17 & No. 18. 1. I have observed, that our Annual Spring-Tydes do happen in March and September, either at the Tyde next before the Suns Ingrefs into the Æquinoctial points of Aries and Libra. Libra, or the next Tyde after, according as the Moon is near her Full or Change, when the Sun thus enters into the said Signs: And then it flows in height about $7\frac{1}{2}$ fathoms, or 45 foot; the lowest Neap-tydes flowing in height 25 foot. 2. We observe also, that the lowest Neap makes the highest Spring, if the North-East Winds hinder not by blowing hard, and so keep back the Tydes; as usually they do when they blow: whose contrary winds (South-west) if they blow hard, make here the highest Tydes. 3. Concerning our Diurnal Tydes, we observe, that from about the latter end of March till the latter end of September, they are about 1 foot and 3 inches higher perpendicularly in the Evening than in the Morning, that is, if high water happen after the Sun is past the Meridian, or in the Tydes betwixt Noon and Midnight. But from Michael-mas till our Lady-day we find the contrary, the Day-tydes being in that season higher by 15 inches than the Night tydes, or the Tydes between Midnight and Noon. And this proportion holds in both, after the gradual Increase of the Tydes rising from the Neap to the highest Spring, and the like Decrease of their Height till Neap again. 4. As for the highest Menstrual Spring-tyde, that is always the third after the Full Moon or Change-day, if it be not kept back by North-East winds, as it hath been, by my own Observations. 5. I have observed several times, that it flows here on the Change-day, when the Moon is East-South-East, the Tyde flowing in for the space of 5 hours, and ebbing 7 hours; so that there is an hour and an half difference from the Old Tables, which say, it flows but to the Moons being East and West: An Error so great, that by all means it ought to be rectified. 6. There is some difference in reckoning the Tydes by the Moons Bearing on such a point of the Compass on the Full or Change day. For then about that time only will the Rule hold to be exactly true. But from the Change to the Quarters, and from the Full to the Quarters again in the Neap-Tydes, I have observed, it does not flow here by two points of the Compass so long. But concerning the difference betwixt the New and full Full Moon, and the Quarters, Mr. Henry Philipps hath framed a Table for the rectification of this Error in the River of Thames; to be found in Number 34. p. 656, 657. of the Phil. Trans. 7. The water flows nor ebbs equal spaces in equal times, but its Velocity is strongest at the first both of the Flood and Ebb, and so gradually decreaseth until FullSea or Low water. This is observ'd in Spring-Tydes only, as you may see by the following Table, which I have made from my Observations of our Tydes here. To make them always so near as to half inches, is neither easie, nor material, or usefull. But this hath been likewise observed, that it hath flowed or ebbed at the first of the Tyde one foot in 6. minutes, or that then the Tyde ran out a foot in 6. minutes, or did rise so much in height. The Tyde-Table by Hour-quarters. | Hours & quart. Feet Inch | Hours & quart. Feet. Inch | |--------------------------|--------------------------| | 1 — 2 — 7½ | 1 — 2 — 7½ | | 2 — 2 — 6 | 2 — 2 — 6 | | 3 — 2 — 6 | 3 — 2 — 6 | | 1 ... — 2 — 6 | 1 ... — 2 — 6 | | 1 — 2 — 6 | | | 2 — 2 — 5½ | | | 3 — 2 — 5 | | | 2 ... — 2 — 5 | 2 ... — 9 — 0 | | 1 — 2 — 3 | | | 2 — 2 — 3 | | | 3 — 2 — 3 | | | 3 ... — 2 — 3 | | | 1 — 2 — 2 | | | 2 — 2 — 1 | | | 3 — 2 — 1 | | | 4 ... — 2 — 1 | | | 1 — 1 — 9 | | | 2 — 1 — 8 | | | 3 — 1 — 8 | | | 5 ... — 1 — 8 | | For the flowing of 5 hours. For the Ebbing of 7 hours. 45 feet circiter. Y yyyy 2 The Observer did not think it necessary to make everywhere in the Ebbing the like Division, he doth in the flowing hours, alleging for that omission the easiness of such a division, soon made by any body, because of the near agreement betwixt the divisions of both. 8. The usual number of Tydes from New Moon to New Moon, or from the Full to the Full, is Fifty nine. 9. In the River of Severn, 20 miles above Bristol near Newnham, 160 miles from the Rivers mouth (Lundy,) the head of the Floud, at its coming in in Spring-tydes, ariseth in height like a Wall near nine foot high, and so runs for many miles together, covering at once all the Shoales, which were dry before; at which time all Vessels, that lye in the way of the said Head-tydes, or (as it is vulgarly called) Boar, are commonly overset or carried upon the Banks, and the head of the Tyde being past, such Vessels are left dry again. It flows there but two hours, and eighteen foot in height, and it ebbs ten hours. The reason of the said Boar is doubtless the straightening and shoaling of the River in that place, it being there but half a mile broad; as it is but 20 pearches over, three miles higher; running tapering to Gloucester. So far this Observer; To whom as there are due particular acknowledgements for his care of observing hitherto, and for his frankness of communicating; so he is further desir'd to continue his Observations with as much exactness as may be, according to the directions set down in the above mentioned Numb. 18. especially to take particular notice, whether the Annual High-tydes, which he seems to fix on those (be it at New or Full) which happen nearest the Equinox, (be it before or after it) be not always before the Vernal Equinox in March, and upon the New Moon; and always after the Autumnal in September, and upon the Ful-moon Spring-tydes: Forasmuch as by a former relation, imparted by a curious Gentleman, we have been informed, that the Annual highest Tydes about Chepstow-bridge, were at St. David's and Michaelmas-Stream, that is, the one a little before the Vernal, and the other somewhat after the Autumnal Equinox, which agrees also with the Conjecture of a very intelligent Mathematician, who is withal of opinion, that because both are not far from the Equinoxes, (though the one before.) before, the other after) it might well give occasion to think it was depending on the Equinox. Moreover, the curious Reader may be pleased to compare this Account with that, which was given concerning the Tydes observed at Plymouth, Numb.33. p.633. and to take notice, that the difference of the Day-tyde from the Night-tyde, agrees in both, (of which the reason may be considered;) but, as to the difference of the increase and decrease of the Water about Bristol from what Mr. Colepress observed at Plymouth, that may much depend upon the position of the places; that of Plymouth being out to the Sea, this near Bristol being on the Severn far within Land. Whilst the Reader is comparing this Information; with that of the lately cited No.33. he will meet there pag.633. in the last line, with the word perpetual, which he is desired to change into proportional, which indeed should have been intimated much sooner. Extract Of a Narrative, made by an Ingenious English Gentleman, now residing at Seville, concerning his Voyage from Spain to Mexico, and of the Minerals of that kingdom. To pass by many curious Observations touching the Vegetable and Animal Sphere, (which I reserve for another occasion) I shall now entertain you only with some of the Observables, I meet with about Minerals in the kingdom of Mexico whither I travell'd A.1664. under the Character of a Biscaner, by the recommendation of a friend in the same Ship, that carried thither a New Vice-roy of Mexico, remaining in that Country almost two years in continual studies and researches, especially about Minerals and their Generation, Separation, &c. And indeed Nature hath so prodigally enriched this Country with all sorts of Minerals, both perfect, imperfect and mixt that she almost overwhelms the Observation of the most diligent and most curious Naturalists. I have dealt with the skilfullest Miners in those parts, but I found them to know of, and care for little in the matter of Minerals, but Gold and Silver. Some of them shew'd