An Account of a Doubler of Electricity, or a Machine by Which the Least Conceivable Quantity of Positive or Negative Electricity May be Continually Doubled, Till It Becomes Perceptible by Common Electrometers, or Visible in Sparks. By the Rev. Abraham Bennet, M. A.; Communicated by the Rev. Richard Kaye, LL.D. F. R. S.

XXVII. An Account of a Doubler of Electricity, or a Machine by which the least conceivable Quantity of positive or negative Electricity may be continually doubled, till it becomes perceptible by common Electrometers, or visible in Sparks. By the Rev. Abraham Bennet, M.A.; communicated by the Rev. Richard Kaye, LL.D. F.R.S. Read May 10, 1787. The great importance of a machine for the purpose of detecting very minute quantities of electricity has occurred to many of the cultivators of this science; as by such an assistant not only many chemical combinations or solutions, but also many yet unexplained atmospherical phenomena, may become intelligible. The labours of M. Volta have been very successful on this subject by the application of his condenser (as he terms it), which, by means of a thin-coated electric, is capable of receiving a greater quantity of the electrical fluid than a common insulated conductor, and rendering it perceptible by separating the positive and negative sides of the charged plate. On this ingenious contrivance Mr. Cavalllo made a very considerable improvement by transferring the received quantity of electricity from a larger to a smaller condenser, as explained in the Phil. Trans. Vol. LXXII. Notwithstanding the very great sensibility of this apparatus, the electricity of the atmosphere is sometimes too weak to be discoverable by it: for instance, in some showers, when the negative state of the falling rain is nearly equal to the positive state of the air. Add to this the trouble of keeping an insulated and elevated conductor sufficiently dry, and the dan- ger of it in a thunder-storm. I therefore contrived the following doubler for the purpose of more easily making an electro-meteorological diary, which I undertook at the request of my friend Dr. Darwin, who hoped, that from thence some lights might be thrown on the causes of the sudden changes of aerial currents, a circumstance of so much importance to the early growth and maturity of vegetation. I place upon my electrometer, described in a former Part of the Philosophical Transactions, a circular brass plate, three or four inches in diameter, polished and thinly varnished on the upper surface. On this I place another brass plate, of equal diameter, polished and varnished on both sides, with an insulating handle attached to one edge of it. A third plate is also provided, of equal diameter, polished and varnished on the under side, and with a perpendicular insulating handle from the center of the upper side, similar to those mentioned in the Appendix to my last Paper. The method of collecting electricity from the atmosphere, and continually doubling it as much as required, is as follows. If the weather be dry, I carry into the open air a lighted torch, not liable to be easily blown out, or a small lantern with a lighted candle in it, to the bottom of which is fixed, by means of a socket, an insulating handle of glass covered with sealing-wax; in the other hand is carried a coated phial: then, elevating the flame a little higher than my head, I apply to it the knob of the phial, holding it in this situation about half a minute. Then returning into the house (where the above described doubler is kept dry, by being placed on a table not far from the fire), I apply the knob of the phial to the under side of the first plate, which lies immediately upon the electrometer, and at the same time touching the second plate with a finger of the other hand. Then laying aside the phial, I lift up the the second plate by its insulating handle, and if the electricity be not now sensible by the electrometer, I place the third plate, by means of its insulating handle, upon the second plate, thus elevated: then touching the third plate, by stretching a finger over the juncture of its insulating handle, and again withdrawing the finger, I then again separate the third plate from the second. In this situation it will be apparent to electricians that two of the plates are of one kind of electricity, and nearly of equal quantity, and one only of the other. I then apply the third plate to touch the under surface of the first plate which remains on the electrometer, and at the same time covering the first plate with the second, I then touch the second plate by stretching a finger over the juncture of its insulating handle; and first taking away the third plate, and then withdrawing my finger from the second, and lifting it up from the first plate, the electricity becomes doubled. If by this first operation the quantity of electricity does not become sensible by the electrometer, I repeat the process to ten or twenty times, which, by doubling it every time, makes visible the smallest conceivable quantity of electricity, since, at the twentieth operation, it is augmented to above 500,000 times. And though in description the above process of doubling to twenty times may appear tedious, yet when the operator can perform it with sufficient readiness (which is soon acquired) it takes less time than 40 seconds. The collection of electricity from the air, and the touching and position of the plates, are represented in Tab. XI. figures 1. 2. 3. 4. 5. and 6. If it be required to produce sparks, the plates are to be placed upon an insulating stand, without an electrometer, and the process repeated as above till the sparks appear. The experiment which proves that the electricity is doubled by each operation is this. If the two slips of pendulous leaf gold gold of the electrometer be made to diverge to a certain distance by the above process, that distance will be nearly doubled by repeating the operation. Another proof of this duplicate accumulation is, that, when the third plate is applied to the first, the divergency of the leaf gold is apparently undiminished, though in this situation their electricity is diffused over double the quantity of surface. That flame will collect electricity better than points was mentioned in my former Paper, and is very evident if two phials of equal capacity are exposed to the air, the one furnished with a sharp point, and the other having its knob applied to an insulated flame, and their electricity afterwards examined by the doubler. If the weather be rainy, an insulated umbrella may be carried in one hand, and the knob of the phial applied to the upper and insulated part of the handle; and if it rains so slowly as not sufficiently to communicate electricity to the umbrella, a torch is carried under the umbrella, and used as described above. It is obvious that some caution is necessary in managing experiments of so much nicety, since, by the least friction of the hand on the varnished sides of the plates or insulating handles, or if the metallic side of one plate be accidentally rubbed against the varnished side of the other, some degree of electricity is produced, which, becoming sensible by the operation of doubling, may render the experiments equivocal. To obviate these inconveniencies, I join a conducting handle, by means of an insulating nut, to each of the plates. This handle consists of turned unbaked mahogany, about three inches long, into one end of which is inserted a nut of baked wood, about half an inch long, covered with sealing-wax, upon the other end of which nut the brass socket of the plate is fixed; by this means it is not necessary to touch the sealing-wax. wax of the insulating nut, but occasionally to stretch a finger over it to touch the plate, whilst the mahogany handle is held in the same hand. Having found, by repeated experiments, that two clean metallic plates, or two equally varnished plates, rubbed together, produced no electricity, I varnished the second plate on both sides, but more thinly than when one side only was varnished, and in some experiments used thimbles on the ends of the touching fingers. In this way the inconveniencies of accidental friction were in some measure obviated, but much less than I first expected; for, notwithstanding the utmost care, electricity is produced without previous communication: therefore, in experiments requiring the electricity to be often doubled, its communication may yet be ascertained by applying it to the first and second plates alternately; so that positive electricity communicated to the first plate appears positive by the electrometer; but the same electricity, applied to the second plate whilst the first is touched, produces negative in the electrometer. I beg leave to add, that this method of doubling either positive or negative electricity, as well as M. Volta's condenser, with Mr. Cavalllo's improvement on it, as also the ingenious experiments of Father Beccaria with double plates of glass, which he separated after charging, are all of them to be explained from the same principles with the Leyden bottle, of which they may be all said to be only different applications. I shall not therefore trouble the Society with any further theory on this subject, but proceed to lay before them the diary which I have hitherto kept, and during which time I have found no difficulty in collecting electricity from the atmosphere positive or negative, so as to become sufficiently sensible by the above described apparatus, though the hygrometer has sometimes shewn the greatest degree of moisture. Diary | Time of observation | Weather | Winds | Barometer | Thermometer | Hygrometer | Electricity | |---------------------|--------------------------|----------------|-----------|-------------|------------|-------------| | **1787.** | | | | | | | | Jan. 23. 11 o'clock morning | Cloudy | W. moderate | 29.3 | 44 | 0 | Positive | | 24. ½ past 10 morning | Thin clouds | N. moderate | 29.44 | 42 | 0 | Positive | | 25. 11 morning | Thin clouds | E. gentle | 29.51 | 37 | 0 | Positive | | 25. 12 at night | Hard frost and aurora borealis | E. gentle | 29.56 | 38 | 0 | Positive | | 26. 11 morning | Clear frost | N. gentle | 29.5 | 38 | 0 | Positive | | 26. ½ past 8 at night | Beginning to snow | N.E. brisk | 29.5 | 37 | 0 | Positive | | 27. 11 morning | Cloudy and likely to snow | N.E. gentle | 29.2 | 35 | 0 | Positive | | 28. 10 morning | Snowing | S.E. strong | 28.8 | 28 | 0 | Positive | | 28. 40 min. past 12 noon | Snowing very little | S.E. brisk | 28.5 | 28 | 0 | Positive | | 28. 11 at night | Fair, but over-cast | S. gentle | 29.06 | 37 | 0 | Positive | | 29. 10 morning | Small rain and mist on the hills | S. brisk | 29.06 | 38 | 3 | Negative | | 29. ½ past 10 morning | Rain ceased | D° | 29.06 | 38 | 3 | Positive | | 29. 3 afternoon | Few drops of rain | S. strong | 29.06 | 41 | 5 | Positive | | 30. 45 min. past 10 morning | Fair, but over-cast | S. strong | 29.45 | 44 | 6 | Positive | | 30. 11 morning | D° | D° | 29.44 | 46 | 7 | Positive | | 31. 10 morning | Fair and clear | S.W. gentle | 29.55 | 44 | 3 | Positive | | Feb. 1. 9 morning | Thick mist with fine drops of rain | Calm | 29.53 | 46 | 2 | Positive | | 1. 11 morning | Thick mist | S.W. gentle | 29.4 | 44 | 1 | Positive | | 2. 11 morning | Thick mist | S.W. gentle | 29.4 | 44 | 1 | Positive | | 3. 10 morning | Heavy clouds | S.W. brisk | 29.2 | 46 | 3 | Negative | | 3. ½ past 11 morning | Small rain | S.W. strong | D° | D° | D° | Positive | | 4. 8 morning | Clear and frosty | Calm | 29.3 | 42 | 0 | Positive | | 5. ½ past 10 morning | Thick mist on the hills | S.E. gentle | 29.26 | 38 | 0 | Positive | | 6. 10 morning | Thick mist and few drops of rain | S. gentle | 29.12 | 40 | 1 | Positive | | 7. ½ past 10 morning | Cloudy | S.W. brisk | 28.7 | 46 | 5 | Positive | | 7. ½ past 2 afternoon | Small rain | S.W. brisk | 28.69 | 47 | 4 | Negative | | 8. ½ past nine morning | Clear and frosty | Calm | 29.28 | 40 | 0 | Positive | | 9. 12 noon | Cloudy after rain | S. strong | 28.75 | 46 | 4 | Positive | | 9. ½ past 1 afternoon | Rain | S. strong | 28.68 | 46 | 4 | Negative | | 10. 9 morning | Rain | S. gentle | 28.64 | 44 | 1 | Negative | | 11. 12 noon | Beginning to rain | S. brisk | 28.34 | 42 | 2 | Negative | | 12. 12 noon | Fair, with heavy clouds | S. strong | 27.8 | 44 | 2 | Positive | | 13. ½ past 9 morning | Very small rain, thin clouds | N.W. brisk | 28.1 | 44 | 1 | Negative | | 14. and 15. absent. | | | | | | | | 16. 10 morn. | Small rain | S.W. gentle | 28.83 | 47 | 3 | Negative | | 17. 10 morning | Very few thin clouds | W. gentle | 29.42 | 44 | 0 | Positive | | 18. 1 afternoon | Few white clouds | W. brisk | 29.42 | 48 | 1 | Positive | | 19. 11 morning | Few distant clouds | N.W. gentle | 29.53 | 47 | 1 | Positive | | 20. 11 morning | Over-cast | N. gentle | 29.47 | 46 | 1 | Positive | | 21. 3 afternoon | Heavy clouds | N. gentle | 29.42 | 47 | 1 | Positive | | 22. 11 morning | Few white clouds | N.E. gentle | 29.4 | 40 | 0 | Positive | | 23. ½ past 10 morning | Over-cast | E. brisk | 29.38 | 40 | 1 | Positive | | 24. 10 morning | Clear and frosty | S.E. gentle | 29.32 | 42 | 0 | Positive | | 25. ½ past 12 noon | Few clouds | N.W. strong | 29.23 | 46 | 1 | Positive | | 26. ½ past 10 morning | Clear | S. gentle | 29.3 | 45 | 0 | Positive | | 27. mentioned afterwards | | | | | | | | 28. ½ past 12 afternoon | Few white clouds | W. strong | 29.07 | 48 | 0 | Positive | | Mar. 1. 2 afternoon | Few drops of rain | S.W. strong | 28.68 | 50 | 3 | Negative | | 2. 10 morning | Small rain | S.W. very strong | 28.35 | 47 | 4 | Negative | N. B. The thermometer and hygrometer were placed where they were not likely to be altered by fixed up three years and upwards, during which time its index has moved within... ### Mr. Bennet's Description of a Doubler of Electricity. #### Diary of atmospherical Electricity. | Winds | Barometer | Thermometer | Hygrometer | Electricity | Instruments to collect | Number of times doubled, a | |----------------|-----------|-------------|------------|-------------|------------------------|---------------------------| | W, moderate | 29.3 | 44 | 0½ M | Positive | Torch and bottle | Plate once lifted up. | | N. moderate | 29.44 | 42 | 0¾ M | Positive | Ditto. | | | E. gentle | 29.51 | 37 | 0¾ D | Positive | Ditto. | | | E. gentle | 29.56 | 38 | 0¾ D | Positive | Ditto. | | | N. gentle | 29.5 | 38 | 0¾ D | Positive | Ditto; no stronger than before. | | N.E. brisk | 29.5 | 37 | 0¾ D | Positive | Umbrella | Doubled. | | N.E. gentle | 29.2 | 35 | 0¾ D | Positive | Torch and bottle | Plate once lifted up. | | S.E. strong | 28.8 | 28 | 0¾ D | Negative | Umbrella and torch | Ditto. | | S.E. brisk | 28.5 | 28 | 0¾ D | Positive | Torch and bottle | Doubled. | | S. gentle | 29.06 | 37 | 0¾ M | Positive | D° | | | S. brisk | 29.06 | 38 | 3½ M | Negative | D° | Plate once lifted up; divergency of the leaf gold very great. | | S. strong | 29.06 | 41 | 5½ M | Positive | D° | Ditto, but weaker. | | S. strong | 29.45 | 44 | 6½ M | Positive | D° | Four times doubled. | | S.W. gentle | 29.55 | 44 | 3½ M | Positive | D° | Plate once lifted up. | | Calm | 29.53 | 46 | 2½ M | Positive | D° | Ditto. | | S.W. gentle | 29.4 | 44 | 1¾ M | Positive | Umbrella and torch | Three times doubled. | | S.W. gentle | 29.4 | 44 | 1¾ M | Positive | Kite | Strong sparks were produced from a string 260 yards long, | | S.W. brisk | 29.2 | 46 | 3½ M | Positive | Torch and bottle | Plate once lifted up, very strong. | | S.W. strong | 28.7 | 46 | 5½ M | Positive | D° | Ditto, also very strong. | | Calm | 29.3 | 42 | 0¾ D | Positive | Umbrella | Twice doubled; a few minutes after the torch was tried, | | S.E. gentle | 29.26 | 38 | 0¾ M | Positive | Torch and bottle | Plate once lifted up. | | S. gentle | 29.12 | 40 | 1 M | Positive | D° | Ditto, strong. | | S.W. brisk | 28.7 | 46 | 5½ M | Positive | Torch and bottle | So strong as twice to strike the sides of the electrometer, | | S.W. brisk | 28.69 | 47 | 4½ M | Negative | Umbrella | Plate once lifted up. | | Calm | 29.28 | 40 | 0¾ M | Positive | Torch and bottle | Ditto. | | S. strong | 28.75 | 46 | 4 M | Positive | D° | Ditto. | | S. strong | 28.68 | 46 | 4½ M | Negative | Umbrella | Ditto. | | S. gentle | 28.64 | 44 | 1¾ M | Negative | Umbrella | Ditto. | | S. brisk | 28.34 | 42 | 2 M | Negative | Torch and bottle | Ditto. | | S. strong | 27.8 | 44 | 2½ M | Positive | D° | Ditto. | | N.W. brisk | 28.1 | 44 | 1¾ M | Negative | D° | Ditto; 10 minutes after the rain ceased the electrometer was | | S.W. gentle | 28.83 | 47 | 3½ M | Negative | D° | | | W. gentle | 29.42 | 44 | 0 | Positive | D° | | | W. brisk | 29.42 | 48 | 1 M | Positive | D° | | | N.W. gentle | 29.53 | 47 | 1¾ M | Positive | D° | | | N. gentle | 29.47 | 46 | 1¾ M | Positive | D° | | | N. gentle | 29.42 | 47 | 1¾ M | Positive | D° | | | N.E. gentle | 29.4 | 40 | 0¾ D | Positive | D° | | | E. brisk | 29.38 | 40 | 1¾ D | Positive | D° | | | S.E. gentle | 29.32 | 42 | 0¾ D | Positive | D° | | | N.W. strong | 29.23 | 46 | 1 M | Positive | Lantern | Just sensible to the electrometer, without the doubler. | | S. gentle | 29.3 | 45 | 0¾ D | Positive | Lantern | More sensible, the lantern being elevated fifteen feet high. | | W. strong | 29.07 | 48 | 0 | Positive | Lantern and bottle | | | S.W. strong | 28.68 | 50 | 3¾ M | Negative | Umbrella | Often doubled; a few minutes after rain ceased, and the | | S.W. very strong| 28.35 | 47 | 4½ M | Negative | Umbrella and torch | Plate once lifted up. | *Note:* The hygrometer consisted of fifteen feet of string, during which time its index has moved within the space of 14 inches, which is therefore divided into inches. | Number of times doubled, and other observations. | |------------------------------------------------| | Plate once lifted up. | | Ditto. | | Ditto. | | Ditto, no stronger than before. | | Ditto; a strong bottle was this day tried, which appeared to collect as well as any. | | Doubled. | | Plate once lifted up. | | Ditto. | | Doubled. | | Plate once lifted up; divergency of the leaf gold very great. | | Ditto, but weaker. | | Four times doubled. | | Plate once lifted up. | | Ditto. | | Ditto; the hygrometer was higher than known during above three years. | | Ditto. | | Three times doubled. | | Strong sparks were produced from a string 260 yards long, with brass wire in it. | | Plate once lifted up, very strong. | | Ditto, also very strong. | | Twice doubled; a few minutes after the torch was tried, when the rain had ceased, and a much stronger positive was produced. | | Plate once lifted up. | | Ditto, strong. | | So strong as twice to strike the sides of the electrometer, and sensible without the plates. | | Plate once lifted up. | | Ditto. | | Ditto. | | Ditto. | | Ditto. | | Ditto. | | Ditto. | | Ditto. | | Ditto; 10 minutes after the rain ceased the electrometer was weakly negative, and 5 minutes after that strongly positive. | | Ditto. | | Ditto. | | Ditto. | | Ditto. | | Ditto. | | Ditto. | | Ditto. | | Just sensible to the electrometer, without the doubler. | | More sensible, the lantern being elevated fifteen feet high. | | Four times doubled. | | Often doubled; a few minutes after rain ceased, and the electrometer became positive. | | Plate once lifted up. | The hygrometer consisted of fifteen feet of whipcord, suspended horizontally: it has been divided into inches, which is therefore divided into inches and eighths, moist and dry. The atmospherical electricity was sometimes so strong as to need no doubling, and mostly required only one application of the second plate, yet I frequently found it necessary to repeat the process from two or three to twenty times. Perhaps the exact comparative quantity of electricity residing in the atmosphere might be measured by the number of operations required to render it perceptible by the electrometer, all other circumstances being cautiously attended to. If the electricity of the atmosphere should happen to be much weaker than I have yet found it, there remains not only the resource of doubling oftener, but the capacity of the instruments may be much increased; as, first, by using a larger flame; secondly, by elevating it higher; thirdly, by collecting the electricity with a very thin glass ball, silvered within, and coated on the outside in the common way, or gilt; fourthly, by grinding and polishing the plates of the doubler very exactly; fifthly, by making the experiments in an advantageous situation. In all these particulars my apparatus was defective, yet amply sufficient for the discovery of the atmospherical electricity. After considering the successful effect of flame, in collecting atmospherical electricity, I placed an insulated lantern upon a pole about fifteen feet high, and suspending a gold thread from the lantern connected it with the electrometer, and was agreeably amused with seeing the pendulous gold leaf open and shut with every passing cloud. On the 27th of February, 1787, when there was a considerable mist whilst the lantern was thus elevated, the leaf gold frequently struck the sides of the electrometer; and, in Mr. Bennet's Description, &c. about an hour, some drops of rain beginning to fall, the appearance of electricity with this apparatus entirely ceased, though I elevated the lantern several times in the course of the day.