411 



the granular quartz is supposed to pervade the base of the mountain 

 to an indefinite depth, the corrections, in proportion to the mere dif- 

 ference between the specific gravities assumed by Dr. Hutton and 

 that found by experiment, were simple in comparison to those ne- 

 cessary on the second hypothesis ; but in each case the attractions 

 of opposite portions of the cylindrical sections became, in fact, un- 

 equal, and consequently required to be computed with due regard 

 to their respective specific gravities, as well as the azimuth and alti- 

 tude 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 selec- 

 tion of granite mountains, if possible, for this purpose, because their 

 homogeneity might be presumed with considerable confidence. 



Observations and Experiments on Vision. By William Charles Wells, 

 M.D. F.R.S. Read July 4, 1811. [Phil. Trans. 1811, p. 378.] 



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 se'en 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 ob- 

 jects, 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 occa- 

 sions a dilatation of the pupil, it appeared to Dr. Wells not impro- 

 bable that it might also affect other muscular powers of the eye. It 

 was his intention to have made this experiment on his own eyes ; 



