Geological Society. 75 



the exposed surfaces. We cannot, therefore, conclude, as already 

 observed (4), that the capacity of the plate is twice that of the 

 sphere. 



19. The following experiments are further adduced in support 

 of the preceding : — 



Experiment 17. A copper plate 10 inches square, compared with 

 the same plate rolled up into an open hollow cylinder, 10 inches 

 long by 3' 2 inches diameter. Here, as in the last experiments, 

 although the surfaces are actually the same, yet, electrically consi- 

 dered, the plate has twice the surface of the cylinder, one surface of 

 the cylinder being shut up. 



On examining the charges of the cylinder and plate, they were 

 found to be, as in the preceding experiments, as 1 : si 2\ that is, as 

 the square roots of the exposed surfaces, and the intensities in an 

 inverse ratio of the surfaces, which seems to be a general law for 

 closed and open surfaces. 



Experiment 18. A hollow copper cube, side 5*7 inches, surface 

 195, compared with a hollow copper sphere of diameter equal side 

 of cube, surface 103 square inches nearly. 



On examining the charges of the sphere and cube, they were 

 found to be as 9 : 10 nearly, charge of the sphere being 9 circular 

 inches, under an intensity of 10°, and charge of cube being 10 cir- 

 cular inches, under the same intensity of 10°. The charges of a 

 cube, and of a sphere whose diameter equals the side of the cube, 

 approach each other, notwithstanding the differences of the surfaces, 

 owing to the six surfaces of the cube not being in a disjointed or 

 separated state. 



20. The author observes, in conclusion, that the numerical results 

 of the foregoing experiments, although not in every instance mathe- 

 matically exact, yet upon the whole were so nearly accordant as to 

 leave no doubt as to the law in operation. It would be in fact, he 

 observes, assuming too much to pretend in such delicate experiments 

 to have arrived at nearer approximations than that of a degree or 

 two of the electrometer, or within quantities less than that of 25 of 

 a circular inch. If the manipulation, however, be skilfully conducted, 

 and the electrical insulations perfect, it is astonishing how rigidly 

 exact the numerical results generally come out. 



GEOLOGICAL SOCIETY. 

 [Continued from vol. xxviii. p. 562.] 

 Nov. 23, 1864.— W. J. Hamilton, Esq., President, in the Chair. 

 The following communications were read : — 



1. " On the occurrence of Organic Remains in the Laurentian 

 Rocks of Canada." By Sir W. E. Logan, LL.D., F.R.S., F.G.S., 

 Director of the Geological Survey of Canada. 



The oldest known rocks of North America, composing the Lau- 

 rentide Mountains in Canada, and the Adirondacks in the State of 

 New York, have been divided by the Geological Survey of Canada 



