Mon. June 18 [1776]. 1R + 3B + C + 2A comm. to 7 rows = (341), & el. to a given mark on pith el. gives shock equal or rather greater than 1 row el. to same degree and not commun. to rest. IR + 3B + C + 2A elect. to 1 on straw el. and comm. to rest always passed through 1 loop of machine. The same elect. to 1 sometimes passed, sometimes failed. 1 row charged to 1 and not commun. to any more passed 3 times through 5 loops without once failing. 1R + 3B + C + 2A el. to 1 and comm. to rest would never pass through 2 loops. 611] 2nd Leather torpedo tried under water with metals with glass tubes on them, all rows charged to 4 gave briskish shock, which was much greater than shock out of water with 1 row to 12, but rather less than with 2 rows to Do. The shock received in same manner with 1 row not communicated to rest was less when el. to 1, and about equal when el. to 21. With 7 rows el. to 1 shock of D° Torp. when received through the salted lime tree wood gave slight shock about equal to 3A passed through same wood without torpedo. Charge of 7 rows el. to 4 is to that of 13 row el. to 1 as 7 x 2.8 : 1 :: 12 to 1. 612] Tu. July 4 [1775]. 2nd leather torp., the wire belonging to convex side fastened to outside of battery and inside of battery touched by wire of flat side. 3 rows of battery charged to 1 and comm. to remainder. Under water no sensible diff. whether I touched convex or flat side with one hand. Out of water, touching tail with one hand and one side of one elect. organ with metal, a much greater shock if I touched convex side than flat side. The event was the same if it was elect. by neg. elect. Touching convex side of both organs with one hand only, standing on electrical stool, a shock in that hand, but I think scarcely so strong as under water. Touching flat side in same way, much the same. Laying 1 finger on convex surface of one organ & another finger of same hand on the middle of the convex surface, a very slight shock. [Probably June 19, 1775.] Laying one finger on convex surface of one organ & the other on the nearest edge of the torpedo, a considerably greater shock, but not strong. Laying one finger on convex and another on flat side of same organ, a considerably greater shock, but do not know how to compare it in point of strength with that taken the usual way. Tried without any torpedo". 613] 3B being comm. to 7 rows and passed through 1 loop of 26 links of small chain. If the chain was not stretched by any additional weight, the shock did not pass. If the middle link was stretched by a weight of 7 pwt. it passed, & the light was visible in a few links. If it was stretched by a weight of 13 pwt. no light was seen. There was no remarkable difference in the strength of the shock, whether it was received through chain tended by 13 pw. or without chain. The chain was fastened to the same machine that was used in a former experiment, it was 7.9 inc. long and the distance of the supports 5.1. The room was quite dark, it being tried at night without any candle in the room. 3 rows of battery were elect. till pith el. sep. to 1, its el. was then comm. to the rest of the battery, & I received the shock of 1 row, the elect. having its choice whether it would pass through my body or through some salt water. I then elect. 1 row of battery till pith el. sep. to same degree, and commun. its elect. to rest of battery and received the shock of 5 rows of it in same manner. The shock seemed to be nearly of same strength, perhaps rather less. Therefore shock of 5 rows elect. to a given degree seems about equal or perhaps rather less than that of 1 row el. to 3 times that degree. 614] The mean thickness of the section of the elect. organ in the section given in Mr H. † paper, in which the breadth is 10.3 inches, that is, the same as my torpedo's, is 1.3 inc.; the area of one organ is 121 151 2.5 × 51 × = 9 sq. inc., as found by cutting out a piece of paper of that size and weighing it. And according to Mr H. there are about 150 partitions in 1 inch, therefore comp. charge both organs reckoned in old way is 19 × 1.3 × 150 × × 150748000, and the real charge is 1122000 inches of el. supposing the par [Art. 437.] [Anatomical observations on the torpedo. By John Hunter, F.R.S., [Phil. Trans. 1773]. Art. 436.] 1 titions to consist of plates of white glass inc. thick, which is about 2 times as much as my battery, that being = 451000 inc. el. 615] Tried with the 2nd leather torpedo, new covered, in large trough full of water, the torpedo laid flat as in figure, the electrical organ being (as supposed) 3 inches under water. was just sensible in elbow. If torpedo was tried out of water with 1 row to 1 comm. to 7 and touched with hands in usual manner, the shock was just felt in hands, and if touched with metals, Tried under water in above-mentioned manner with 7 rows el. to 4, the upper surface being touched with the pestle of a mortar held in one hand, the other hand dipt into water as far as wrist, a shock in the wrist of the hand in the water I believe full as strong as the former. The place where the hand was dipt into water was about 11 inc. from the front of the fish, and conseq. about 14 from elect. organ. Tried in the same manner as before, except that the fish lay in an open wicker basket*, just big enough to receive it, and which had been soaked for some days in salt water. The shock seemed much the same. Holding hand in water in same manner as before without touching torpedo-no sensation. With three rows to 1 out of water, the shock was stronger if I touched convex side with one hand laid flat on elect. organs than if I touched flat side in same manner, but the difference was not great. Charge of 7 rows el. to 4 is to that of 1 row el. to 1 as 19·6 to 1. The water appeared by its spe. gra, to contain of salt. 1 * [Art. 421.] RESISTANCE TO ELECTRICITY. 616] Comparison of conducting power of salt and fresh water in the latter end of March and beginning of April, 1776. Tried with Nairne's last battery, 6 jars being chose, each of which held very nearly the same quantity of electricity; the wires run into the bent ends of the tubes being made to communicate with the outside of the battery, and the wires run into the straight ends being fastened to separate pieces of tinfoil. The six jars were all charged by the same conductor: the communication with that and each other was then taken away, and the jars discharged through the tubes, one after the other, by touching the abovementioned bit of tinfoil by metal held in one hand, and the wire of the jar by metal held in the other hand, the shock being received alternately through each tube. Straw electrom. = 4. scarce sensibly just sensibly less = Th. 57. [Resistance = 390000 Ohms.†] Resistance of 4.7 inches in tube 15 supposed equal to 407 in 14. Therefore sat. sol. conducts 8.6 times better than salt in 69 of water. The same solution tried in tubes 22 and 23. Exp. 2. Tube 23 22 3.3 41 5.5 electrom. at 11. Th. = 58. [R. = 118000]. † sensibly greater. less in same proportion. 4.4 inches in tube 23 41 in tube 22. Therefore sat. sol. conducts 8.94 times better than salt in 69 of water. * [Saturated solution of sea salt.] +[The resistance of the saturated solution in Ohms. calculated from the measurements in Art. 635 by Kohlrausch's data, is given for each tube within brackets to indicate the absolute value of the resistances compared.] Exp. 3. A new saturated solution and solution in 69 of water made and tried in tubes 15 and 14. [R. = 390000.] Therefore new saturated solution conducts 9.61 times better than new solution in 69. Exp. 4. Salt in 69 of water compared with salt in 999 of water in Resist. 41 in tube 23 supposed equal to 411 in 22. Therefore salt in 69 conducts 9.57 times better than salt in 999. Exp. 5. Salt in 999 compared with distilled water in tubes 12 and 20. [R. = 462000.] diff. more sensib. than in 1st trial. supposed right. = Therefore salt in 999 conducts 36-3 times better than distilled water. 1.9 3.3 2.55 3. Th. = 58°. The distilled water changed for rain water. Therefore rain water conducts 24 times better than distilled water, or 15.2 times worse than salt in 999. it. The rain water changed for distilled water with zoo of salt in Therefore salt in 20000 of distilled water conducts [3.67] times better than distilled water, or 9·92 worse than salt in 999. |