a collision with a molecule of the opposite kind n times in a second, then the average velocity will be half that which the force can communicate to the molecule in the nth part of a second. According to the theory of Clausius, it is only a small proportion, say 1/p, of the molecules, which, at any given instant, are dissociated from molecules of the other kind, so as to be free to move under the action of the electromotive force, so that we must suppose each of the free molecules to continue free for a time pT; but since the proportion of free molecules to combined ones is quite unknown, the only definite result we can obtain from Kohlrausch's data is a certain very small time T, such that if the electromotive force acted on the molecules of the component during the time T, it would impress on them a velocity twice their actual average velocity. Since the time T is very small, it is more convenient to speak of the molecule being brought to rest n times in a second, and to calculate n. On the Ratio of the Charge of a Globe to that of a Circle of the same Diameter. The true value of this ratio is = 1.570796.... Cavendish has given several different values as the results of his experiments. In the account of his experiments, which represents his most matured conclusions, he states this ratio as 1·57 (Art. 237). All the other values, however, either as stated by Cavendish or as deducible from his experiments, are lower than this. In Art. 281 the charge of the globe of 12.1 inches diameter being 1, that of a circle 18.5 inches diameter is given as 992. The ratio of the charge of a globe to that of a circle of equal diameter as deduced from this is 1.542. In Art. 445 the charge of the globe is compared with that of a pasteboard circle of 19.4 inches diameter. Cavendish gives the actual observations but does not deduce any numerical result from them, which shows that he did not attach much weight to them. As they seem to be the earliest measurements of the kind, I have endeavoured to interpret the observations by assuming that the positive and negative separations were equal when the observations are qualified in the same words by Cavendish. I thus find 14.2 or 14.3 for the charge of the globe, and 15.2 for that of the circle, and from these we deduce for the ratio of the charge of a globe to that of a circle of equal diameter 1·5054. In Art. 456 the ratio as deduced by Cavendish from the observations on the globe and the tin circle of 18.5 inches diameter is 1.56. From the numerical data given in the same article, the ratio would be 1.554. Cavendish evidently thought the result given here of some value, for he quotes it in the foot-note to Art. 473. Another set of observations is recorded in Art. 478, from which we deduce the ratio 1.561. It appears by a comparison of Arts. 506 and 581 that Cavendish, at the date of the latter article (which is doubtful), supposed the ratio to be 1.5. (See foot-note to Art. 581.) At Art. 648 the ratio is stated as 1·54. At Art. 654 measures are given from which we deduce 1.542 and 1.37. The numbers in Art. 682 are the same as those in Art. 281. ALPHABETICAL INDEX. The references are to the Articles. A. A, coated plate of glass so called, "First A, Double 333, 451, 455, 461, 478, 483, Epinus (Franz Ulrich Theodor, b. 1724, Basket salt 628 Beech 590, 609 Bees'-wax 336, 371, 376 Brass plate of trial plate 297 Breaking of electricity through plates C. Calc. S. S. A. 626, 694 and note 34 Canal 40, 68, 69; bent 48, 49, 84-95 Canton, John, F.R.S. (1718--1772) 117, Cement 303, 484, 497 Centre of suspension 388 Chain machine 433, 605, 613 Charge defined 237; does not depend see Tables; of battery 412; divided Charging jar 223, 225 Circles 273 Circuit, divided 397, 417 Coated plates 300, 314, 441; theory of, 74, 160, 169; lists of, see Tables 133 Column 145-147 Communication 100, 219; of charge to Comparison of charges 236 Compound plate 379-381, 560, 677— Compression (or pressure) 179; distin- guished from condensation 200 Conduction by hot glass 369 Conductivity 469, 491; of straws 565 Cone, attraction on particle at vertex 7 Contact 306; impossible 196 note; of Copper wire, resistance of 636-646 Crown glass 301, 330, 378, 411, 430, Cylinder 54, 148-151; charge of 281, D. D, coated plate 483, 487 Deficient fluid 67, note Canal 40 Communication 100 Deficient fluid 67, note Distance of spreading 328 Inches of electricity, circular 458, 648; Degrees of electrification 329, 356; of Dividing machine 341, 459, 517, 591 E. and F. 457 E. Earth connexion 258, 271 Electric organ of torpedo 396, note 29 Electrification, degree of 102, 201 and Electrodes, large 258, 271 Cavendish's discharging 402, 405, 427, gauge (paper cylinders) 224, 248, 295, Divisions of 560, note Henly's 559, 568, 570, 571, 580; on Lane's 263, 329, 559, 569, 570, 571, 580, 589, 603, 604 Paper cylinders 486 Straw 249, 404, 559, 570, 571, 581; General conclusion 291 Glass, different electric qualities of 301, Glass house 378 Glauber's salt 626, 694 Globe, charge of compared with that of 681, 687, note 35 Globe, electrified 20-27, 280; capacity Globe, meaning the world 214 Globe of electrical machine 248, 495, Globe within hemispheres 218, 512, 562, Globes, coated 523, 542, 559, 563 H. Hamilton, Dr, Prof. of Philosophy, Heat, effect on charge of glass, &c. 366, Henly (William, F.R.S., d. 1779); linen Hissing noise before spark 213 Hot glass a conductor 369, note 26; Hygrometer corks 459; Smeaton's 468; I. Immoveable fluid 12, 351 Inches of electricity 458, 648, 654 Increase of charge of globe due to in- duction 339, 652 and note 24 |