525 OBSERVATIOIStS AND EXPERIMENTS ON VISION. 



The belladonna It will, perhaps, be thought extraordinary, that Dr. 

 SJomethtng Cutting's eye in its relaxed state, before the application of 

 more than sus- the belladonna, brought parallel rays to a focns anterior to 

 fn<^i>owe^ ^^^'the retina; but that similar rays met in a point upon the 

 retina, while the eye was under the full influence of that 

 substance; as it may hence seepi, that the belladonna had 

 done more than merely suspend the exercise of the power, 

 hy which the eye is fitted to see near objects distinctly. An 

 observation drawn from the former state of my own sight 

 will, I expect, make this matter plain. 

 Different ap- When I enjoyed the faculty of adapting my eyes to ob- 

 ftars on the'eye J^^*^ ** different distances, the rays of a star, which was 

 viewed attentively by me, always met in a point a little be- 

 fore the retina*; whence I at first concluded, that tny eye 

 •was unfit for accurate vision by parallel rays. But I after- 

 ward found, that if I looked at a star carelessly, its rays 

 had then their concourse on the retina. In the former case, 

 from long habit, originating in my having chiefly viewed 

 near objects with attention, some small exertion was made 

 for the accurate view of a distant object, though none 

 was requisite; in the latter, all demand for exertion ceas- 

 ing, ray eye fell into the most relaxed condition, that by 

 which it was fitted for parallel rays. Dr. Cutting's eye 

 ^eems to have been similar to what my own once was, in re- 

 gard to such rays ; but as he had not acquired the faculty 

 of viewing a distant object, without making some exertion, 

 the rays from a star crossed one another in his eye before 

 they came to the retina. The capacity, however, of mak- 

 ing any exertion was taken away by the belladonna, and 

 pencils of parallel rays were, in consequence, brought to 

 points upon that membrane. 

 Effects of age JV. Being now in possession of a new instrument, I next 

 onsipr sig . g^j^gjyip^g^ ((, gal„^ |jy means of it, some illustration of the 

 changes, which the vision of short-sighted persons under- 

 goes from age. 

 General mis- It has been very generally, if not universally, asserted 



take respectkig jjy, systematic writers upon vision, that the short-sighted 

 ^rc rendered by age fitter for seeipg distant objects thaa 



♦ Essay on Single Vision, &c. p. 138. 



they 



