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 11⁄2, 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 11⁄2 as 3184 to 8909, and that to make pith separate 54 to that to make straw separate 1 as 2920 to 8909. Jars 1 and 2 being electrified by wire and jar 6 by coating till pith electrometer separated 11⁄2 and a communication being then made between 53 them in the manner used for trying Leyden vials, pith balls separate 5 51 5 (1316+ negative, therefore charge of jar 6 should be 1273. 7 Charge of 1+ 2+ 3+ 4 = 12544. Jars 1+ 2+ 3+ 4 being compared in the same manner with jar 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 = 1. 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 :: 1-444n - 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. =1·5 circ. inc., as Cavendish seems to do here.] + [Art. 413.] 584] M. 6. Electricity of 1st row of old battery was reduced to by touching 11 times by crown glass of 10 inches square. Therefore charge of 1st row to that of crown glass as 153 to 1. The first row of new battery appeared by that means to contain 107, the 2nd row 11, and the 3rd 11.4 times the charge of the same plate. The mean area of the convex coating of each jar seemed to be 14 × 12 = 175 inches, to which adding 5, id est of area of bottom, whole coating may be estimated at 180 square inches of same thickness as sides. 12 (10 Elect.2 row of new battery was reduced to by touching 101 (13.94 (13.94 (10) times by jar 1, therefore charge = jar 1 × 1466, and charge mean row jar 1 x 14.18 = 45149 inc. el. * [See Art. 506.] [Here A seems to be the charge of one of the first 4 jars taken as unit, B that of one of the others taken as 4, and R that of the row taken as 22, the battery being 151, as in M. 2.] 585] M. 7. Whether shock of battery is sensibly diminished by imperfect conduction of the salt water in the jars. An uncoated glass jar like the coated ones was filled with fresh water and put into a glass jar of fresh water, a brass wire with knob being put into it, and a slip of tinfoil into the outer jar, it was charged till straw electrometer separated to 8 and tried by shock melter* filled [with] sea water, wires about 3 inc. dist. The water in inner jar was then changed for sat. sol. s. s.† and that in outer for about equal parts of D° and fresh water, and tried in the same manner. The shock seemed rather greater, but was plainly less when electrometer was at 7. When shock was taken without shock melter* it was as strong with el. at 5 as with D° at 8. Jar 2 being charged to 8 and its electricity communicated to jar, the electrometer separated to 41. 586] M. 8. Feb. 28, 1775. Specific gravity bottle filled with salt water from torpedo trough weighed 8.4.18 by ingraved weights. Th. at 49. Specific gravity = 1.0254. Being mixed with 70073525 its weight of rain water, specific gravity bottle weighed 8.4. 1, Th. at 49, specific gravity 1.0190. Excess of specific gravity above unity of stronger is to that of weaker as 1.335 to 1. The quantity of salt in them is as 1·3524 [to 1]. Therefore the excess of specific gravity above 1 differs pretty nearly, but not quite, in as great a ratio as the quantity of salt in them. M. 9. April 1. D° Specific gravity bottle with water from torpedo trough weighed 8. 4. 22 by D° weights. April 29. Torpedo trough filled with water to within 1 inch of top, and 58 oz. salt added. Specific gravity bottle filled therewith, Th. at 70°, weighed 8. 4. 12. At 54 same water weighed 8.4.161. One bottle of sea water weighed 8.4. 11, Th. at 67. Another bottle weighed 8. 4. 191⁄2, Th. Do. Specific gravity bottle with rain water weighs 8.1.221. [M. 10 blank]. * [This word occurs also in Arts. 622 and 637. See facsimile at Art. 622.] + [Saturated solution of sea salt.] M. 11. Rule for finding the quantity of salt in water by its specific gravity. Let the specific gravity of the solution at 46 = S, and quantity of salt solution 587. In 2nd Lane's electrometer or 1st detached do. = 40 threads screw = 1 inches, or 1 division of plate inch. Weight of the unsalted ones on June 18, and number of vibrations of a pendulum inches long, in which the electricity of 1 row of the battery was reduced from 2 to 1 by pith balls by touching with them, the ends being wrapt round with tinfoil fastened on with gum. [Mr Vernon Harcourt, in his Address to the British Association (B.A. Report, 1839, p. 48), has given extracts from Cavendish's MS. on Heat, p. 1 to p. 50, but he does not mention any page 98.] + [Art. 609.] + [So in MS. |