Dr, Wollaston's Microscopic Doublet, 255 



object as the scales of the Podura, for example, decidedly suffer 

 in their performance. I have, therefore, always expressed my 

 conviction, that simple microscopes with large apertures and 

 good figures, of the ^i^^, -yi^, ^, and -^iy, &c., of an inch focus, 

 beat engyscopes of equal power *. Such being the result of my 

 experience, I must confess, that when I hear opticians speaking 

 with triumph and exultation of having made an engyscope 

 magnify some 7000 times, I lose all patience — what good or 

 useful purpose such preposterous dilatation and dilution of a 

 mere picture can serve, I am wholly at a loss to guess, unless 

 that of exciting the wonder and admiration of the stupid vulgar, 

 at the expense of provoking the ridicule and derision of those 

 who understand the quackery of such practices, be esteemed 

 such. 



The old chromatic telescopes were capable of shewing a very 

 great deal ; and I consider the old compound microscopes, if con- 

 structed in the best manner, to be fully adequate to the task of 

 making an entertaining exhibition of that numerous class of objects^ 

 which is visible with small angles of aperture ; but the makers 

 of them seem determined to evince as hearty a contempt of the 

 science of optics as possible, and consider a large flat field of 

 view as the only circumstance necessary to be attended to in 

 their construction. It is rare to see any but equi-convex 

 glasses employed in them, not one of which ought by right to 

 be used, either for the object or eye-glasses, but the said equi- 

 convex lenses are the cheapest^ and of course the best to get a 

 profit upon. 



In a paper I formerly published ill the old series of this 

 Journal, on False Light (vol. xvii. p. 202), 1 described some 

 object-glasses for microscopes, which consist of a plano-con- 

 vex lens of considerable aperture, with its plane side next the 



* It is not my wish to represent the engyscopes as any better than they really 

 are, and I shall venture to assert that it would be necessary to have a perfect 

 aplanatic object-glass of 5^5 of an inch focus, and the same aperture, in order to 

 obtain a power from it equal to that of j»5 of an inch, which should surpass the per- 

 formance of a good equivalent simple microscope (I should not be surprised if the 

 double object-glasses of ChevaUer should one day be made of this depth, by combin- 

 ing two or three together). I state it as my own private notion, that if two object- 

 glasses are equal in point of aperture and perfection, that the force and decision 

 with which they will exhibit proof objects, is nearly in the direct ratio of their in- 

 trinsic power, that is, one of half an mch focus will perform nearly twice as well as 

 one of an inch focus, &c. 



82 



