VOL. LXXXV.] PHILOSOPHICAL TRANSACTIONS. • 46 1 



judgment of the results, and to correct any error we might fiill into in conducting 

 the experiments. This circumstance will also give to the experiments an addi- 

 tional claim on the notice of the r. s. 



The first experiment was made at 3 o'clock, at which were present Sir Henry 

 Englefield, Mr. Ramsden, and myself. It required some time, and considerable 

 ability, in which I claim no part, to adjust the microscope, and bring the cornea 

 into its field : when this was done, the appearances were so different from what 

 were expected, that we had a difficulty in recognizing the object; all that could 

 be seen was 4 curved lines, but even these were rendered confused by reflections 

 from the cross bars of the sash of the window. On throwing up the sash, the 

 curved lines became very distinct, and that which appeared the inner one in the 

 microscope, was ascertained to be the convex projecting surface of the cornea. 

 This being determined, the person whose eye was the object of the experiment 

 was desired to look at the corner of a chimney at the upper end of Sackville- 

 street, a distance of 235 yards, through the hole in the brass plate, and after- 

 wards to look at the edge of the small hole itself, which was only 6 inches from 

 the eye. In doing this several times, the curved lines were seen to separate from 

 each other ; and the microscope required being withdrawn from the object when- 

 ever the person's eye was adjusted to the near distance ; but the very reverse took 

 place when it was fixed on the distant one. 



In making these experiments, the least motion of the head carried the cornea 

 out of the field of the microscope ; it was therefore necessary that the 1 objects 

 should be exactly in the same line respecting the eye, and that the person should 

 remain silent. When he complied with any request which had been made, he 

 signified by touching the knee of the observer with his hand, that he had done 

 so. This experiment was made on the eyes of all present, and the same appear- 

 ances were uniformly observed ; and after several trials we became so familiar 

 with the appearances, that the observer only required information of the adjust- 

 ment having been changed, to enable him to tell which of the objects the eye 

 was fixed on. 



August the 1 St, about 4 o'clock, these experiments were repeated, and after 

 several attempts were made, without success, to explain the cause of the carved 

 lines, we found it necessary to shade a part of the window, to take off the glare 

 of light which fatigued the eye, and rendered it unsteady ; this made the curved 

 lines less distinct ; and when the whole window was shaded they disappeared al- 

 together, leaving a very distinct view of the whole thickness of the cornea, with 

 a well defined line formed by its anterior projecting surface. This discovery 

 proved the curved lines to be reflections from the sides of the window on the 

 cornea ; but as it was not made till 6 o'clock, we were obliged to pospone any 

 further observations on it. 



