[ 453 ] 



>;yii,)^LVIII. On the Phantascope. By Prof. J. Locke*. « 



AS many persons find it difficult, if not impossible, to con- 

 verge the optical axes (or in common phrase to look 

 " cross-eyed ") for the purpose of making the experinients 

 lately described by met under the head of " binocular vision," 

 I have invented an instrument which enables all persons to 

 succeed in obtaining the chief results. It is very simple. 



i 



I 





E. Eye screen. I. Index-screen. B. Base-board. 



* From Silliman's Journal for March 1850. 

 t Phil. Mag. vol. xxxiv. p. 195. 



