THE MICROSCOPE. 



and vegetable histology were also very great and fruitful, including, as 

 they did, investigations into the minute structure of the nerves, the 

 discovery of the capillaries and the like, and when we consider the 

 difificulties under which he labored, we may well stand amazed at the 

 extent and general accuracy of his discoveries. * * * 

 Dr. Robert Hooker, however, was the first to use a compound micro- 

 scope consisting of a simple objective, a simple eye lens and an 

 intermediate lens, which latter, however, was inserted only to enlarge 

 the field of vision, not to increase its power. An Italian,, Eustachio 

 Divino, constructed an instrument whose tube was " as large as a 

 man's leg," and with an eye-piece "as broad as a man's hand," 

 consisting of two plano-convex lenses joined with their con- 

 vex surfaces, somewhat after the manner of Ramsden's posi- 

 tive eye-piece, used sometimes at the present day for micro- 

 metric work. This mibroscope could be drawn out to four 

 lengths, giving magnifying powers of 41, 90, iii and 

 143 diameters respectively. A few years later a compatriot of his, 

 Fillippo Bonani, first made use of rack and pinion for purposes of 

 adjustment, and of a substage condenser for improving the illu- 

 mination. During the following century improvements were con- 

 stantly made in the construction and mounting of the "simple" 

 microscopes, the most important, perhaps, being that of Nathaniel 

 Lieberkuehn, of Berlin, who placed his object lens in the center of 

 a highly polished concave speculum, by means of which a strongly 

 concentrated illumination is reflected upon the upper side of the 

 object. This method of illumination, as adapted to the modern 

 "compound" microscopes, is still used with apparent satisfaction 

 by some microscopists of the British school. Sir Isaac Newton 

 was the first to propose a " reflecting" microscope; but little seems 

 to have come either of his or of any of the numerous subsequent 

 designs of this character. Indeed with this instrument the great 

 physicist was singularly unfortunate; for though he suggested 

 monochromatic illumination as a means adapted to the correction 

 of the errors arising from spherical and chromatic abberation, he 

 more than offset this help by the publication of his opinion that 

 chromatic lenses were a physical impossibility. * * * * 

 * * But, as in this instance, so many times since have the 

 dogmatic dicta enunciated by great and justly revered theorists, 

 been proved erroneous by the empyric achievements of practical 



