48 Experiments for a new Theory of Ftsion. 



have been a repetition of the quatie, &c. Hence the date of the 

 book must be 1st of the 2(1 month 1456 Ann. Doin. 



Yours truly, 

 Strathendiy, June21, ISiy. Gavin IngliS. 



IX. Experiments for a new Theory of Vision. By Joseph 

 Reade, M'.D. 



:j^ Mr. Tilloch. 



KuWicrra iSriv. Xen, 



Sill, — i ERHAPS no subject in natural philosophy has moreen- 

 gaged the attention of the learned, or claimed more interest, than 

 that concerning the proper seat of vision. For two hundred years 

 the retinal theory has been maintained, and its difficulties, if not 

 absurdities, softened down by tlie learned ingenuity of mathema- 

 ticians and nietaphvsicians. Well aware that to overturn a theory 

 so universally adopted, and stampefl with the seal of antiquity, 

 requires a number of well regulated experiments and legitimate 

 deductions, I now commit my endeavours to the candour of the 

 intelligent reader. 



Exp. 1st.-;— Having often remarked, when examining the eyes 

 of patients, that surrounding objects, such as a lighted candle, 

 &c. were painted on the transparent cornea in a beautiful and 

 minute manner, as on the face of a convex speculum, it oc- 

 curred to me that the mind might receive impressions or ideas 

 from those erect images; and I was the more desirous of bringing 

 this interesting suggestion to the test of experiment, in conse- 

 quence of the many difficulties attached to the present system of 

 vision. I now pasted* two narrow strips of black cloth in the 

 shape of the letter T, and about three inches in length, on one 

 of the ui)pcr panes of a large and well-lighted window. I then 

 requested a gentleman with a large pupil and good sight to seat 

 himself about four or five feet from the latter, and to fix his eyes 

 steadily on it. Looking into iiis pupil I perceived the letter T to 

 be mimitely yet distinctly painted by reflexion. I then took a 

 plano-convex lens in my right hand, such as school-boys use for 

 burning-glasses, and held it close to the pupil. On again looking 

 at the corneal image of the letter T, I perceived it enlarged or 

 magnified in all its dimensions, and the spectator said, he also 

 perceived it much larger than with the naked eve. On removing 

 the lens a little further from his eye, I perceived the letter on the 

 pupil not only magnified, but surrounded with colours; and now 

 the spectator saw the letter large, confused, and surrounded with 

 colours. So far the phenomena of vision answered exactly to 



the 



