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. It was found that when the straw electrometer separated to 1 + 0, I 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. 1 142 = 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 sea salt and distilled water. The shock of 1 jar charged till the straw electrometer separated to (8 11.0 1+0, discharged through a column of 10 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 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 water was (greater than through 23 of the mixed. 12.0 By the mean, the resistance of 1·3 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. It was found that the shock of one jar, charged till the straw electrometer separated to 1.01, passed through a column of the salt water in diminished than in passing inches long, was rather more less 27.7) tube 7, 21.25 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 24.4 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 X = 1.06 to 1 nearly, the 22.3 37.4 shock should be as much diminished in passing through a column 22.94 long in tube 9 as through one of 24.4 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 They were made to lap 10 inch long. 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 stood at 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: The distance at which Lane's discharges with a given jar is nearly proportional to the quantity of electricity in the jar, for if a jar is charged to a degree at which Lane is found to discharge at a given distance, and its electricity is communicated to another jar of the same size, so as to contain only as much electricity as before, Lane will then discharge at nearly the former distance. M[EASURES]*. 581] M. 1. Comparative charges of jars and battery↑. If jar 1 is electrified till straw electrometer separates to 1, and its electricity is communicated to jars 2+ 4, pith electrometer separates 53. Therefore charge required to make pith balls separate 5 is to that required to make straw electrometer separate 1 as 3184 to 8909, and that to make pith separate 5 to that to make straw separate 11⁄2 as 2920 to 8909. 53 Jars 1 and 2 being electrified by wire and jar 26 by coating till pith electrometer separated 1 and a communication being then made between them in the manner used for trying Leyden vials, pith balls separate 5 (1316+ 5 negative, therefore charge of jar 6 should be 1273. Jars 1+ 2+ 3+ 4 being compared in the same manner with jar 6 the pith balls did not separate at all. M. 2. If the charge of jars 1 + 2 + 3 + 4 is called 4 Jar 8 being electrified it was found that it must be touched 7 times by white cyl. to reduce the quantity of electricity to. The 4 jars must be touched 8 times by do. Therefore charge of jar 8 = 31. A piece of crown glass 1 foot square of which weighed 10-12 was coated with tinfoil about 10 inches square. * [These "Measures" are on a set of loose sheets of different sizes marked M. 1 to M. 21, and another set marked M. 1 to M. 12.] + [Art. 411.] [These numbers are given as in the MS. They should be each multiplied by 10. See also Art. 585, where the numbers seem to be deduced from some other experiment.] M. 3. The charge of each row of the battery was found by charging to a given degree by electrometer and touching it repeatedly with jar 4 till the separation of electrometer was reduced to that answering the charge. to *The 1st, 2nd, 3rd, 4th, 5th, 6th, 7th row required to be touched 18, 19, 17, 18, 17, 17, 18 times, therefore charge and charge of whole battery = 180 times that of jar 4 and real charge = = 321000 and if real charge by computed of white glass = 7.5, computed charge = 42800 which answers to 187 square feet of glass whose thickness = 10. 7 Therefore charge of jar 4 answers to 1.04 square feet of D° thickness. The coating is about of a square foot, and therefore the mean thickness = = .058. 582] M. 4. Let jar be touched n times † by jar which is to first as x to 1, it will be reduced in ratio of 1 to (1+x)", therefore if it is reduced to thereby Rule for finding ratio of charge of 2 jars, supposing the charge of first to be reduced to by touching n times by 2nd. Charge of 1st is to that of 2nd :: 1444n- to 1. *N.B. The left-hand row is supposed to be called the 1st row. [If Jar 4=2675 circ. inc. (See Art. 506) whole battery = 481500 circ. inc. or 321000 glob. inc., counting 1 glob. inc. 15 circ. inc., as Cavendish seems to do here.] + [Art. 413.] |