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V. A nam Tlieory of 'Telescopes founded on rational Principles 

 and interesting Experiments. By J. Reade, M.D.* 



T OOKING on the corneal theory of vision as established, 

 -^ in this paper I shall endeavour to apply that theory to 

 practical advantage in the science of astronomy. Although 

 I have shown, by numerous and I may venture to say con- 

 clusive experiments, that our ideas of objects are produced by 

 erect images painted on the pupil, still 1 by no means argue 

 that the retina is not the nerve communicating with the sen- 

 sorium, in a similar manner as the nerves minister to feeling, 

 hearing, tasting and smelling. Indeed, the five senses may 

 be all reduced to one, the sense of feeling. So long as philo- 

 sophers believed that inverted images painted on the retina 

 produced the pha?nomena of vision, so long the most incon- 

 sistent opinions were advanced of long- and short-sightedness, 

 and the theory of telescopes, spectacles, &c. " If the cornea 

 or crystalline (say authors), or either of these, be too flat, a 

 pencil of light coming from an object at an ordinary distance 

 will have its focus at some point beyond the retina, and there- 

 fore vision will be indistinct, as in the case of an object too 

 near for a common eye." Let us for a moment examine this 

 reasoning. It is admitted on all hands, that no inverted 

 image is ever formed, until the rays cross after arriving at 

 the focus; consequently, if the focal point were situate beyond 

 the retina, no image could ever be painted on that substance, 

 and we must be driven to the absurdity, that the mind could 

 perceive an object without an image. Dr. Porterfield has 

 some strange metaphysical ideas on this subject, at one time 

 talking of pictures on the retina, and the next moment deny- 

 ing their existence. Having examined the eyes of many short- 

 sighted persons with much accuracy, I find them not to differ 

 in the least from long-sighted eyes; hence the flatness or 

 plumpness of the cornea can have nothing to do with the dis- 

 ease, however necessary it may be to the refracted theory of 

 philosophers. 



Here I may enlarge on this subject, but must refer to a 

 former paper in your valuable Journalf, wherein I have ex- 

 perimentally demonstrated that focal images are not formed 

 by any crossing of the rays, when passed through a lens, 

 but that the focus is produced by reflected images uniting, 

 and sent from the concave sides. Indeed, I am inclined to 

 think that we must look to the nerves for the cause of short- 

 sightedness, and not to any fanciful flatness or plumpness of 



* Communicated by the Author. 



t See Phil; Mag. vol. lviii. p. 249, and vol. lix. p. 200. 



the 



