462 . PHILOSOPHICAL TRANSACTIONS. [aNNO 1795. 



August the 3d, at 7 o'clock in the morning, Mr. Ramsden and myself resumed 

 our experiments, Sir Henry Englefield being unable to attend at that hour. The 

 eye of the person under observation was shaded from the light by shutting the 

 half of the window-shutter directly before it, and to direct the sight to pass 

 through it, a hole was bored in the shutter ; the other half of the shutter was 

 turned back, so as to take off the side light, only letting in enough to illuminate 

 the cornea ; in this state the cornea was very distinctly seen, and the former ex- 

 periments were repeated on it, with a micrometer wire in the focus of the eye- 

 glass, so placed as accurately to oppose the anterior edge of the cornea. The 

 motion of the cornea became now perfectly distinct ; its surface remained in a 

 line with the wire when the eye was adjusted to the distant object, but projected 

 considerably beyond it when adapted to the near one ; and the space through 

 which it moved was so great as readily to be measured by magnifying the divi- 

 sions on a scale, and comparing them ; in this way we estimated it at the 800 

 part of an inch, a space distinctly seen in a microscope magnifying 30 times. 

 It may not be improper, for the sake of accuracy, to mention that the hole made 

 in the window-shutter did not admit of seeing up Sackville-street, so that the 

 distant object was now only at QO feet, which is rather less than is necessary for 

 parallel rays ; a circumstance, so far as it can be considered, in favour of the ex- 

 periment, as a more distant object must have increased the effect on the cornea. 

 Having satisfied ourselves fully respecting the result of this experiment, we de- 

 sisted from further trials. 



At 12 o'clock of the same day, we prevailed on Sir Henry Englefield to make 

 the experiment on my eye, without giving him any information on the obser- 

 vations that had been made in the morning. He was very much struck with 

 the distinctness of the cornea ; and told me without difficulty the different ob- 

 jects to which my eye was adjusted, and was as fully satisfied as either Mr. Rams 

 den or myself with the result of the experiment. Mr. Ramsden now made the 

 same experiment on Sir Henry's eye, but was unable to retain it in the field of 

 the microscope ; the motion of the cornea was always in one direction, and very 

 irregular ; after repeated trials, equally unsatisfactory, the eye became so fatigued 

 that he was obliged to desist. 



August the 4th, Mr. Ramsden repeated the experiment on Sir Henry's eye, 

 to ascertain if possible the cause of his former want of success, and found the 

 same circumstances again take place ; the curve of the cornea moved always in 

 the same direction, never returning to the wire. This could not be accounted 

 for, till it was accidentally discovered to arise from the motion of his hand in 

 touching the knee of the observer, for when that was omitted, the experiment 

 was followed by the same results as those made on the rest of the company. I 

 have been more particular in mentioning this circumstance, as it shows that the 



