50 BORDER LINES OF KNOWLEDGE 



in one of the lectures before the Medical Class, sub- 

 sequently communicated to the American Academy 

 of Arts and Sciences, and printed in its " Transac- 

 tions " for February 14, 1860. I refer to the appar- 

 ent transfer of impressions from one retina to the other, 

 to which I have given the name reflex vision. The 

 idea was suggested to me in consequence of certain 

 effects noticed in employing the stereoscope. Profes- 

 sor William B. Rodgers has since called the attention 

 of the American Scientific Association to some facts 

 bearing on the subject, and to a very cmious experi- 

 ment of Leonardo da Vinci's, which enables the ob- 

 server to look through the palm of his hand (or seem 

 to), as if it had a hole bored through it. As he and 

 others hesitated to accept my explanation, I was not 

 sorry to find recently the following words in the " Ob- 

 servations on Man" of that acute observer and thinker, 

 David Hartley.* 



" An impression made on the right eye alone by a 

 single object may propagate itself into the left, and 

 there raise up an image almost equal in vividness to 

 itself; and consequently when we see with one eye 

 only, we may, however, have pictures in both eyes." 

 Hartley, in 1784, had anticipated many of the doctrines 

 which have since been systematized into the theory 

 of reflex actions, and with which I have attempted 

 to associate this act of reflex vision. My sixth ex- 

 periment, however, in the communication referred to, 



• Vol. L p. 207. London, 1801. 



