THE MICROSCOPE. 



opticians. ***** Lieberkuehn also con- 



structed the first "solar" microscope for projection of magnified 

 objects upon large screens; and the same was equipped with the 

 movable mirror to admit of its protracted use by a Mr. Cuff, of 

 London, where Lieberkuehn first exhibited his invention. But the 

 high hopes engendered by it were never realized, partly, no doubt, 

 on account of its dependence upon direct sunlight — always an 

 uncertain factor, especially in England — but more particularly 

 because it can only display the shadow of things, instead of the 

 objects themselves. It still survives, however, in a modified and 

 improved form, as the oxy-hydro and electric light projection micro- 

 scopes which, though valueless for the purposes of original investi- 

 gation, are of great use for the demonstration of certain classes of 

 objects, to large numbers at one time. ***** 

 Baker described also a new invention for fixing the pocket micro- 

 scope [an instrument strongly resembling the toy grandiloquently 

 advertised and extensively sold some four years ago as the "Craig" 

 microscope] and giving light to it by a speculum, this instrument 

 having been originally intended to be used by holding it up to the 

 light like afield glass. ***** A certain Mr. 

 Marshall appears to have constructed the first compound micro- 

 scope, according to our modern conception of the term, and of this 

 various modifications were made from time to time, among which 

 should be mentioned those of Culpepper and Scarlett, as well as 

 those of the Adamses, father and son; which latter continued the 

 favorite instrument until displaced by the "achromatic," which we 

 owe to the demonstrations of Euler, the great Swiss mathematician, 

 as corrected and seconded by the practical experiments of John 

 Dolland, who showed the corrective power of crown glass refraction 

 over flint glass dispersion. Yet as late as 182 1 we find the great 

 French philosopher, Biot, insisting that "opticians regard the con- 

 struction of a good achromatic microscope as impossible," and 

 at the same time Dr. Wollaston — the highest authority upon 

 this subject then in England — gave it as his opinion "that 

 the compound microscope would never rival the simple 

 one, * * * yg|. jp ]ggg |.}^^j^ lyfQ years thereafter 

 two French opticians, Selignes and Chevalier, produced the reductio 

 ad absurd um of all this a priori theorizing in the shape of compound 

 achromatic objectives, consisting each of two or more pairs of 



