its choice whether it would pass through my body or some salt water, the wires in the salt water being brought within such a distance that the shock was weak when taken by the blunt body. I then found that if I took it with the point I could scarce perceive any spark. The experiment was tried in the same manner with a large jar. The shock was very sensibly less though the point was approached almost as fast as I could. 573] Whether shock of one jar is greater or less than that of twice that quantity of fluid spread on four jars *. It was found that if the jars 3 and 4 were electrified in a given degree, and their electricity communicated to the jars 1 and 2, the shock produced by discharging them was nearly the same, or of the two rather more, than that produced by discharging the jar 1 or 2 by itself. The shock of the jar 3 was found to be very sensibly greater than that of jar 4. It was tried with the wooden rod, the jars to be electrified being placed in contact with the tinfoil thereon, and when they were sufficiently electrified those to which the electricity was to be communicated being approached till they touched the rod, all four standing on the same tin plate. The jars were electrified till the straws separated 9 inch. N.B. The jars 1 and 2 contain pretty nearly the same quantity of electricity and their sum is nearly equal to the sum of jars 3 and 4. The quantity of electricity in jar 3 exceeds that in jar 4 in the ratio of 37 to 27, or of 4 to 3 nearly t. 574] Comparison of the diminution which the shock receives by passing through water in tubes of different bores, and whether it is as much diminished in passing through 9 small tubes as through the same length of one large tube the area of whose bore is equal to that of the 9 small ones+. Nov. 1773. It was tried whether a shock was as much diminished by passing through a glass tube filled with water, 37 inches of which held 250 grains of water, as in passing through 9 tubes, 37 inches of all which together held 258 grains of water, the length of water which it passed through being the same in both cases, namely about 40 inches. Two jars were used, and charged till the straw electrometer separated to 3 + 0. The water in the tubes was mixed with a very little salt, and the shock just enough to be perceived. I could not be certain that there was any difference, but if any, that with the single tube seemed greatest. The shock was then made to pass through 7 of the small tubes, 37 inches of which hold about 200 grains of The shock was then sensibly less than with the large tube. water. * [Art. 406 and Note 31.] + [Art. 685.] [See Art. 506.] It was afterwards tried through what length of a tube, 37 inches of which held 44 grains, the shock must pass, so as to be as much diminished as in passing through 441 of the large one. It was found that when it passed through 5·2 inches the shock was sensibly greater, and when it passed through 8-4 sensibly less than with the large one, so that it is supposed it would be equal if it passed through 6.8. so that the resistance should seem as the 1.08 power of the velocity. N.B. The quantity of water which the tubes held was not measured very exactly. 575] The tubes used in p. 123 [Art. 574] were measured by ☀ and are as follows: 37 inches of the 9 first tubes, which are what was used in p. 123 [Art. 574], held together 3373 grains, therefore the shock was very nearly the same, but if anything rather greater when it passed through one tube, 37 inches of which held 3480 grains of, than when it passed through 9 tubes, 37 inches of all which together held 3373 grains. By p. 124 the shock is as much diminished in passing through 6.8 inches of a tube, 37 inches of which hold 567 grains, as through 441 of one, 37 inches of which hold 3480, so that resistance should seem as the 1.03 power of the velocity. 576] Comparison of diminution of shock by passing through iron wire or through salt water*. In order to compare the conducting power of iron wire and salt water, the shock of two jars had its choice whether it would pass through * [Art. 398 and Note 32.] 2540 inches of nealed iron wire, 12 feet of which weighed 14.2 grains, or through my body, each end of the iron wire being fastened to a pretty thick piece of brass wire which I grasped tight, one in one hand and the other in the other, and with them discharged the jars. I It was found that when the straw electrometer separated to 1 + 0, just felt a shock in my wrists, and when it separated to 2 + 0, I felt a pretty brisk one in them but not higher up. I then gave the shock its choice whether it would pass through my body, or 5.1 inches of a column of a saturated solution of sea salt contained in a glass tube, 1 inch of which holds 9-12 grains of fresh water, the wires running into the salt water being fastened to brass wires as before. I found the shock to be just the same as before, and found too that increasing the length of the column of salt water not more than of an inch made a sensible difference in the strength of the shock. Therefore the electricity meets with the same resistance in passing through 2540 inches of wire whose base is inches of salt water whose base is 9.12. 142 1 = 78 × 144 79 as through 5.1 Therefore, if the resistance is as the 108 power of the velocity, the resistance of iron wire is 607000 times less than that of a column of salt water of the same diameter *. 577] Comparison of conducting powers of saturated solution of seu salt and distilled water. .8 The shock of 1 jar charged till the straw electrometer separated to 1+01⁄2, discharged through a column of 18 inches of a mixture of saturated solution of sea salt with 99 of distilled water in tube 6, was (greater than when it was discharged through 35 inches of saturated less solution of sea salt in tube 2. .87) By a former experiment, the shock passed through 1.35 of the mixed water was (greater than through 40 of saturated solution. By a mean, the resistance of one inch of the mixed water is equal to that of 38 of the saturated solution, therefore allowing for the different bases of the tubes, the resistance of the mixed water is 39 times greater than that of the saturated solution. •55 The shock of two jars, charged to 4 + 0, and discharged through 1.8 [If the resistance is as the velocity, resistance of saturated solution of salt is 355400 times that of iron wire. By Matthiessen and Kohlrausch it should be about 502500. See Note 32.] (greater than when it was discharged of distilled water in tube 5, was (8 By a former experiment, the shock passed through of distilled Sgreater water was less than through 23 of the mixed. 12.0 By the mean, the resistance of 13 of distilled water = that of 231 of mixed. 10.9 inches of tube 5 in the place where used holds 120 grains of, or 37 inches holds 408 grains, which is the same as tube 8: therefore the resistance of distilled water is 18 times greater than that of mixed, or 702 times greater than that of a saturated solution of sea salt. 578] Whether the electricity is resisted in passing out of one medium into another in perfect contact with it. The 9th tube of P. 126 [Art. 575] was filled with 8* columns of saturated solution of sea salt inclosed between columns of, the end columns being. The tube 7 was filled with one short column of at the bent end, and a long column of saturated solution of sea salt. 27.71 inches long, was rather (more less It was found that the shock of one jar, charged till the straw electrometer separated to 101, passed through a column of the salt water in tube 7, diminished than in passing through the mixed column in tube 9, the wires used in tube 9 being immersed in the end columns of, and those used in tube 7 being immersed one in the short column of at the end and the other in the column of salt water. The length of the mixed column in tube 9 was 43.5 inches, its weight was 10.5, the weight of a column of of the same length was 18.10, therefore the sum of the lengths of all the columns of salt water was 21.8 inches, and by the experiment the shock was as much diminished by passing through 244 inches of salt water in tube 7 as through this. But as the bore of tube 7 in that part which was used was greater than tube 9 in the ratio 24.4 36 22.3 37.4 = 1.06 to 1 nearly, the shock should be as much diminished in passing through a column 22.94 long in tube 9 as through one of 244 in this. Therefore the shock is as much diminished in passing through a mixed column, in which the length of salt water is 218 inches, as through a single column of the same size whose length is 22-94 inches. The difference is much less than what might proceed from the error of the experiment. 579] A slip of tin was made consisting of 40 bits soldered together, all inch broad and all about inch long. They were made to lap Perhaps 80.] [8% in MS. about inch over each other in soldering. I could not perceive that the shock of a jar was sensibly less when received through this than through a slip of tin of same length and breadth of one single piece. If the jar were charged pretty high and a double circuit made for it, namely through this piece of tin and my body, I could not perceive the least sensation. 580] Made at Nairne's with his large machine. A long conductor was applied to the electrical machine and a smaller conductor to its end, a Henly's electrometer was placed on the middle of the long conductor, and a small jar with a Lane's electrometer fastened to it was made to touch the short one. When Henly's The jar was then changed for one of rather more coated surface and a much smaller knob. When Henly's stood at 30 or 35, Lane's discharged at 177 650, so that Lane's discharged at nearly the same distance with the same charge, whichever jar was used. = Henly's electrometer was then placed on an upright rod, touching the long conductor near the furthest end, Lane's electrometer with the first jar being placed as before. Henly then rose to 55 or 60 before Lane discharged at 17·55 = ·681 inch. Henly being then lifted higher it rose to 65, Lane remaining as before. It was then lifted still higher, when it rose to = Lane's being then separated to 27.55 1.060, the jar once discharged over surface of glass and once to the electrometer, but there seemed reason to think that Henly's rose no higher than before, namely 65. My Henly's electrometer usually rose to 90 when Lane's discharged at 12.20467 inches. Therefore the distance at which Lane's discharges, answering to different numbers on Henly's, is as follows: |