loo THE MICROSCOPE. 



The microscope in its simplest form is but a convex lens of any- 

 transparent medium whose refractive index is greater than that of 

 air. Nature supplies them at every turn — every dew-drop reveals 

 the minute anatomy of the leaf upon which it trembles; and many a 

 bright lad has become oblivious to the parchedness of his tongue, as 

 in reaching after the well filled tumbler his thirst of mind was sud- 

 denly quenched by visions of startling beauty within it. A lens of 

 rock crystal taken from the ruins of Norwich was exhibited before 

 the British association at Belfast in 1852 ; and there is treasured at 

 the museum of the Portici an ancient lens of glass with a focal length 

 of only one-third of an inch. But the earliest employment of the 

 microscope as an instrument of scientific research, though traced 

 back definitely to the latter part of the sixteenth or the beginning of 

 the seventeeenth centuries, cannot now be assigned with any degree 

 of certainty to any one individual or country, even. * * * 

 Zacharias Jansens & Son, of Amsterdam, are said to have manufac- 

 tured them as early as 1590, and it is believed to have been one of 

 their instruments that Drebbel brought with him to England. It 

 was an imposing affair ; a copper tube six feet long contain- 

 ing the lenses ; and was mounted upon three brass dolphins 

 which rested upon a base of ebony. ***** 

 In 1656 Dr. Robert Hooke, of London, published his famous work 

 entitled " Micrographia Illustrata," in which he describes and illus- 

 trates an immense number of objects as seen through the imperfect 

 instruments of his day; and he describes a method of constructing 

 lenses of great magnifying power in the form of tiny globules of 

 glass. He also seems to have been the first to avail himself of the 

 principle of "immersion." ***** g^^. j.}^g 

 honor of being the first really scientific microscopist should no doubt 

 be accorded to Anthony VanLeuvenhoek, whose numerous highly 

 important discoveries were all made with the most primitive instru- 

 ments, constructed by himself, consisting (not of spheres or globules) 

 but for the first time of a double convex lens, provided with ar- 

 rangements for holding the object and regulating its distance from 

 the lens. Of tliese instruments he appears to have made a great 

 number, using each for one or two objects only, and with infinite 

 labor, skill and patience investigating the new world thus opened to 

 his view; thus discovering and describing many of the larger animal- 

 cuke, such as rotifers, vorticellse, etc. His labors in the field of humati 



