ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 



82" 



Fig. 189. 



in the plane of the object supposed to be on the stage. The swinging 

 bar C is provided with rackwork F on which the arm H, carrying 

 the condenser E (which might be a 1-inch or 2-inch objective), can be 

 moved up or down by the milled head D. The arm H is fitted to 

 slide for convenience of centering with the optic axis ; the mirror I is 

 also made to slide for the same purpose. These sliding movements 

 also permit the use of slightly excentrical pencils, which are found to 

 give increased power of resolution in particular cases. The condenser 

 E can be racked to focus the illumination on the object. The lateral 

 swing of the bar C will then provide the whole range of oblique 

 illumination in altitude concentric with the object, by suitable adjust- 

 ment of the mirror. The swinging bar also permits the condenser 

 and mirror to be used above the stage for " opaque " illumination. 



It is obvious that this apparatus admits of application to many of 

 the less expensive forms of Microscope at a very moderate outlay, and 

 that other modifications may be suggested that would add materially 

 both to its efficiency and its cost. We understand that Messrs. 

 Watson have applied a disk at C for registering the angle of obliquity. 

 A centering arrangement with rectangular motions might be advan- 

 tageously applied on H. 



Swift's Radial Traversing Substage Illuminator. — Messrs. Swift 

 have (very advisedly) abandoned the second sector at right angles 

 to the first,* and now issue 

 the instrument in the form 

 shown in Fig. 189. 



We extract (slightly al- 

 tered) the fuUowing remarks 

 which they make as to the 

 relative value of condensers 

 and swinging substages : — 



"This arrangement (Fig. 

 189) is superior to the ordi- 

 nary swinging substage, as it 

 does not in any way impair 

 the steadiness of the upper 

 stage, being slid into a dove- 

 tailed fitting on the limb of 

 the Microscope, in lieu of the 

 substage which is detached. 

 Beyond this it has the advan- 

 tage of being light and handy, 

 and the condenser, if neces- 

 sary, can be brought above 

 the stage for the illumination 

 of opaque objects. We would 

 only, however, recommend 

 this apparatus to those who wish to avoid the tiuuble of using an 

 achromatic condenser, although this latter piece of apparatus when in 



See this Journal, iii. (1880) p. 867. 



