Page:Proceedings of the Royal Society of London Vol 1.djvu/433

Rh In the course of these experiments Dr. Wells observes, that the sympathy between the eyes, which is in general considered as sympathy of the iris, is in fact sympathy of the retina; for when the pupil of one eye is dilated by belladonna, the pupil of the other becomes so much the more contracted, in consequence of the greater light which the enlarged pupil admits.

He remarks, also, that though he has lost, in great measure, the power of adaptation, he has in no degree lost any command of the external muscles, but can make the optic axes meet at any short distance from his face, to which he could formerly make them converge. So also, while Dr. Cutting's eyes were under the inﬂuence of belladonna, the powers of the external muscles remained unimpaired; whence it appears, that the powcr of adapting the eye to diﬁ'erent distances is not dependent on the external muscles, but rather to be referred to the crystalline lens, although the muscularity of that organ does not appear to Dr. Wells to be by any-means established.

Sir Isaac Newton, who ﬁrst considered the ﬁgure of the earth and planets, conﬁned his view to the supposition of their having been originally in a ﬂuid state; and he conceived them to retain the same ﬁgure which they assumed in their prirm'tive condition; and those mathematicians who succeeded him in the same path of inquiry have seldom ventured beyond this limited hypothesis, and have shown, that when a body composed of one uniform ﬂuid revolves about its axis, or even if it consists of several ﬂuids of diﬁ'erent densities, its parts will be in equilibrium, and it will preserve its ﬁgure when it has the form of an elliptic spheroid of revolution oblate at the poles.

But though the supposition of original ﬂuidity of the mass simpliﬁes the investigation, it does not seem to be warranted by what we see of the surface ; for in that case, Mr. Ivory observes, the arrangement of all the heterogeneous matters would have been according to their densities; those least dense occupying the surface with gradual increase of density to the centre; whereas, on the contrary, nothing can be more irregular than the density of such solid parts of the earth as come under our observation. and the elevation of continents above the level of the sea, as well as the depths of the different channels which contain the waters of the ocean.

Moreover, according to the latest and best observations made for the express purpose of determining the ﬁgure of the earth, it :does not appear to be of any regular elliptic form.

Since the hypothesis of Newton is, therefore, not consonant to observation, it became necessary to consider the subject in a more