1820.] a new Theory of Vision. 269 



would be sufficient to invalidate the entire. The next difficulty 

 in this catalogue of difficulties is the power of seeing objects 

 distinctly at difterent distances. It is allowed on all hands that 

 to see an object at different distances, either the retina or the 

 crystalline lens must approach so as to shorten what is called 

 the optic axis ; so that the crystalline, according to this theory, 

 must be a great jumper. To calculate the number of jumps, or 

 miniature leaps, the lens of a general officer would take at a 

 review, miglit puzzle an algebraist, vulgar arithmetic being per- 

 fectly inadequate to the solution. And then an able philosopher 

 has given thousands and tens of thousands of muscles, or wings, 

 if you please to call them so, to this little busy, fluttering thing. 

 Indeed Dr. Young might as well have given muscles to an onion, 

 the lamina? of which, and those of the crystalhne, being very 

 similar. On examining all the different theories, we find them 

 all differing, and perfectly inadequate to the effect. Kepler, 

 two centuries ago, supposed that the contraction of the ciliary 

 processes draws the sides of the. eye towards the crystalline, by 

 which means the eye is lengthened, and the retina pushed to a 

 greater distance from the pupils when we are viewing near 

 objects. Mr. Thomas Young differs from Kepler, Descartes 

 from Young, Haller from Young, with a crowd of others whose 

 opinions I think it unnecessary to mention. 



I remain, Sir, your obedient servant, 



Joseph Reade, M.D. 



P.S. The Editor's observations would be acceptable. 



Article IV. 



Reply to Mr. Holt on Rain-Gauges. By Mr. Meikle. 

 (To Dr. Thomson.) 



SIR, Bcrner's-slreet, Feb. 23, 18S0. 



In the Annals of Philosophy for October last, I gave a very 

 concise but unobjectionable refutation of the mistaken idea 

 which M. Flaugergues and others entertain about the true cause 

 of the difference observed in the quantities of water collected in 

 rain-gauges placed at different heights. I then flattei-ed myself 

 that, by means of a simple diagram, I had brought down the 

 subject to the level of the most superficial inquirer; and, there- 

 fore, did not encumber your pages with a tiresome harangue 

 about a thing so extremely simple and obvious to overy one. 



Some persons, however, seem still to cherish a predilection for 

 their favourite error ; and among these your learned correspond- 

 ent Mr. Holt certainly holds no inferior place ; since in yoxir 



