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multitude of optical organs compofing the eye of the Beetle, as far 

 as the limner was able to difcover their ftrufture by the help of the 

 niicrofcope, with intent, partly to exhibit the great number of thofe 

 optical organs, and partly to lliew that each of thefe organs is 

 of a convex Ihape ; not that I would be underllood to mean, 

 that every one of thefe optical organs is a portion of a fphere;* for, 

 if lb, the Beetle would not be able to difcern obje6ls at any dillance, 

 but that each of them is more flattened than fpherical. 



Upon exhibiting this objedl; to the limner, he compared thefe 

 convexities, or protuberances, to thofe round buttons which are 

 at prefent ufed in men's clothes, and made of that metal commonly 

 called Prince's metal. 



Plate XIV. fg. 1 , A B C D E F, reprefents a part of the tunica 

 cornea, or horny part of the Beetle's eye. ABC denote that part 

 which was contiguous to the head. D E F A reprefent the greateft 

 part of the longell row of eyes on the fuperficies of the tunica cornea ; 

 in which, from D E F to A, I counted more than lixty optical 

 organs ; and, between the fame letters, may be feen how each of 

 thefe optical organs rifes with a kind of protuberance. 



It is well known, that when any object is placed before the 

 microfcope, it mull: be fo adjulled that it may neither be too far re- 

 moved from, nor brought too near to the focus of the glafs, for, in 

 either of thofe cafes, the obje6l cannot be feen diftindly. For the 

 fame reafon, if any perfon is defirous to contemplate objedls through 

 thofe optical organs which are in the tunica cornea of the Beetle, he 

 will find it necellary to alIo\^' a fomewhat greater diftance between 

 the tunica cornea and the focus of the magnifier, fo that the focus of 

 each may (if I am allowed the exprelTion), become united in 

 one poijit, as we do when two convex lenfes are placed one 

 before the other in a frame : and, by this means, he will fee 

 the obje^l multiplied feveral hundred times, by reafon of the great 



* I addrcfs mjfflf here to thofe who have feme knowledge in optics. 



