Page:Proceedings of the Royal Society of London Vol 1.djvu/431

Rh the granular quartz is supposed to pervade the base of the mountain to an indeﬁnite depth, the corrections, in proportion to the mere difference between the speciﬁc gravities assumed by Dr. Hutton and that found by experiment, were simple in comparison to those necessary on the second hypothesis; but in each case the attractions of opposite portions of the cylindrical sections became, in fact, unequal, and consequently required to be computed with due regard to their respective speciﬁc gravities, as well as the azimuth and altitude of each.

The nature of these computations is fully explained by the author, but cannot be understood without reference to the ﬁgures which ac- company them. The resulting density deduced according to the ﬁrst hypothesis is found to be nearly 4'56 ; that deduced by Dr. Hutton having been only 4‘48: but according to the second hypothesis, the difference is far more considerable; the density in this case being 4'87.

This last is nearly a mean between that of Dr. Hutton and the density of 5‘48, which Mr. Cavendish inferred from a very different mode of investigation.

By considering the experiments on Schehallien alone, the density of the earth might be assumed to be between the limits above as- signed. the mean of which amounts to 4'71. Mr. Playfair, however, thinks it desirable that an element so important in physical astronomy should be the result of many experiments, and recommends the selection of granite mountains, if possible, for this purpose, because their homogeneity might be presumed with considerable conﬁdence.

The experiments here described by Dr. Wells were made in con- sequence of an imperfection of sight occurring to his observation, which he has nowhere seen upon record. The subject to whom the disorder happened was a gentleman about thirty-ﬁve years of age, who, after a slight catarrh, had been seized with a degree of stupor, and weight of his forehead, accompanied with a paralytic state of the right eyelid. The pupil of this eye was also observed to be much dilated; and he had lost all power of adapting that eye to near objects, although he could see at a distance with great distinctness. The left eye also became shortly after affected in a slight degree, and in a similar manner.

The nature of the defect became evident by trial of spectacles; for it was found that convex glasses enabled him to read with perfect ease, and supplied the want of the power of adaptation which he had before possessed.

Since the application of the juice of belladonna to the eye occasions a dilatation of the pupil, it appeared to Dr. Wells not improbable that it might also affect other muscular powers of the eye. It was his intention to have made this experiment on his own eycs: