332 



PRACTICAL PHYSIOLOGY. 



[lxxi. 



(/>.) Close one eye, and with the other look through the lioles at 

 the near needle, which will he seen distinctly, while the far needle 

 will be double, but both images are somewhat dim. 



(c.) With another card, while accommodating for the near needle, 



close the right-hand hole ; 

 l> 1^ the right-hand image dis- 



appears; and if the left- 

 hand hole be closed, the 

 left-hand image dis- 

 appears. 



(d.) Accommodate for 

 the far needle ; the near 

 needle appears double. 

 Close the right-hand hole, 

 and the left-hand image 

 disappears; and on clos- 

 ing the left-hand hole, 

 the right-hand image dis- 

 appears. 



{e. ) Instead of using a card 

 K perforated with two holes, use 

 an apparatus so constructed 

 that one hole is covered with 

 a green and the other with a 

 red glass. Repeat the pre- 

 vious observations, noting the 

 disappearance of the red or 

 green image, as the case may 

 be. 



(/.) If desired, the holes 

 in the card may be made one 

 above the other, but in this 

 case the pin looked at must be horizontal. 



{g.) Make three holes in a piece of cardboard, as in fig. 250, a, so that they 

 can be brought simultaneously before one eye, and look at a pin or needle. 

 One sees three images of the needle. On looking at a near object, the needles 

 are in the position h, and at a distant object in that shown in c. 



{h.) Miles' Experiment. 

 ~ (i.) Look at a pin through 



[a pin-hole in a card. Ac- 

 commodate for the pin, move 

 the card to and ho, and note 

 that the pin appear? immov- 

 able. 



(ii.) Accommodate for a 

 distant object beyond the pin, 

 and note that the pin appears to move in the opposite direction to that of 

 the card. 



(iii.) Accommodate for a nearer object, and note that the pin appears to 

 move in the same direction as the card. 



Fia. 249.— Scheiner's Experiment. 



Ill 



Fio. 25a 



