500 



MICROSCOPY. 



nnd well-lighted field, and a long working 

 focus ; and they may be considered a necessity 

 rather than a luxury, where fine work is to be 

 done, and for any use when extreme economy 

 is not imperative. 



The Brucke magnifier, a Galilean micro- 

 scope, consisting of a small two-system achro- 



FIG. 2. ACHROMATIC TRIPLET, MOUNTED. 



matic objective, with a concave eye-lens above 

 acting as an ocular, has long been used on the 

 Continent, but has only lately received de- 

 served recognition in America. Its long work- 

 ing focus, good definition, considerable power, 

 small size, and moderate cost, commend it for 

 the preparing microscope, notwithstanding its 

 small field and rather deficient illumination. 

 Some simple microscopes are supplied, as an 

 extra, with a compound body and ordinary 

 ocular for high-power dissections, or for occa- 

 sional examination of objects. Few preparing 

 microscopes are large and firm enough to em- 

 ploy such an arrangement to real advantage; 



Pis. 8. LENS-HOLDER 



but the Bausch & Lomb Optical Co. have just 

 introduced for the same purpose a little com- 

 pound body, shown in situ in Fig. 4, only 

 three inches long and three fourths of an inch 

 wide, containing a diminutive objective, erec- 

 tor, and ocular, which is light enough for the 



preparing microscope, and capable of giving, 

 by draw-tube adjustment, a range of powers 

 of from 12 to 150 diameters, with a working 

 focus varying inversely from H to i inch. This 

 arrangement is somewhat equivalent to the 

 Brucke magnifier, giving similar working focus 

 and width of field with the same powers. It 

 has the advantage of supplying, by mere slid- 

 ing of its draw-tube, such a range of powers 

 as, with the other magnifier, could only be at- 

 tained by changing or dividing the objective. 



As a lens-holder, to support simple lenses, 

 like the pocket arrangement shown in Fig. 2, 

 for instance, while objects are being dissected 

 or arranged, some recent books recommend a 

 bent wire passed through a cork, which in 

 turn slides up and down upon a larger vertical 

 wire stuck into a block or spool upon the 

 table; and it must be admitted that such a 

 home-made affair is about as efficient, though 

 not as pleasing to the taste, as the neater 

 stands sold everywhere for the same purpose. 

 One of the simplest of the latter is the Lister 

 stand, originally made by Smith & Beck, and 

 lately elaborated into the " Hampden " micro- 

 scope, by the present firm at the suggestion 

 of a distinguished amateur microscopist ("J. 

 E. M. S.," 1882, p. 258). Many varieties are 

 made, especially by the French and German 

 opticians, having a rack-adjustment for the 

 height of the lenses. To gain a greater range 

 of applicability, the writer 

 has devised and used the 

 stand shown in Fig. 3 ("Proc. 

 A. S. M.," 1884, p. 164). It 

 is based upon the model used 

 by engravers, but, unlike that, 

 it is sufficiently firm and man- 

 ageable for either high or low 

 powers, used either near the 

 stand, or at a sufficient dis- 

 tance for the examination 

 of mounted herbarium speci- 

 mens, or of hand - writing 

 upon large papers or books. 

 It consists of a rectangular 

 frame, sliding upon the pil- 

 Inr of a bull's-eye stand (the 

 bull's-eye being often advantageously used in 

 connection with it), with a fine - adjustment 

 screw acting against the pillar above, and with 

 a hinged extension below, giving a total arm- 

 length of seven to nine inches. There is a pair 

 of semicircular jaws to be inserted into the arm 

 for the support of a watch-maker's or en- 

 graver's glass. This stand is equally available 

 for high -power Coddingtons or achromatic 

 triplets, and its range is raised to 100 diame- 

 ters, or more, by adapting to it the Brucke 

 magnifier, or the Bausch & Lomb compound 

 dissecting arrangement. The axis of vision 

 may be set with equal steadiness at any angle 

 from vertical to horizontal, the instrument thus 

 becoming sometimes an efficient aquarium mi- 

 croscope. 



Of complete stands for the simple micro- 



