7 H EXPERIMENTS, &c. 



conceived the position of my eyes to be in the 

 mean while unchanged. To go on with the 

 experiment, when the paper and spot had pro- 

 ceeded to a certain distance from each other, 

 they suddenly came together again ; and this 

 separation and conjunction were alternately re- 

 peated a number of times ; the limits of the 

 separation gradually becoming less, till, at 

 length, the paper and spot both appeared to 

 be at rest, and the latter to be projected upon 

 the middle of the former. I found also, upon 

 repeating and varying the experiment a little, 

 that when I had turned myself from left to 

 right, the paper moved from right to left, 

 and the spot consequently the contrary way : 

 but that when I had turned from right to 

 left, the paper would then move from left to 

 right. These were the appearances observed 

 while I stood erect. When I inclined, how- 

 ever, my head in such a manner, as to bring 

 the side of my face parallel to the horizon, the 

 spot and paper would then move from each 

 other, one upward and the other downward. 

 But all these phenomena demonstrate, that 

 there was a real motion in my eyes at the time 

 I imagined them to be at rest ; for the apparent 

 situation of the spot, with respect to the paper, 

 could not possibly have been altered, without 

 a real change of the position of those organs. 



