118 



SUMMARY OF CUBRENT RESEARCHES RELATING TO 



spherical lens, as applied to this stand by Mr. Tolles for immersion 

 illumination, adds greatly to the facility of obtaining effects of 

 obliquity; indeed, he appears to have been the first to distinctly 



realize the advantages of this kind of illumination, dating back from 

 his first production of immersion objectives, having " balsam angle " 

 greater than 82°. 



Eeflection from the Inside of Body-tubes. *-j-In their new form of 

 stand, Messrs. Sidle prevent the formation of a burnished reflecting 

 surface, produced by friction below the eye-piece, by turning an 

 annular groove on the inner surface of the draw-tube, near the top, 

 of such a width that the surface which is exposed to the friction of 

 the eye-piece will not be uncovered, no matter what eye-piece may 

 be used. 



This device might (Mr. A. L. Woodward considers) be applied to 

 any stand, at comparatively slight expense, whereas the application of 

 a collar would necessitate either a new and larger body-tube or else 

 a narrower eye-piece. 



Whilst on the subject of making this improvement in connection 

 with the eye-piece fitting, we would urge the importance of applying 

 to the various eye-pieces such adapters as will bring the field-lens in 

 each case to the same position in the tube. By this means (as adopted 

 many years ago by Powell and Lealand) the estimation of the mag- 

 nifying power is facilitated, and much of the inconvenience avoided 

 of refocussing and readjusting when different eye-pieces are used 

 with high-power objectives. 



Adaptation of the " Society " Screw to Draw-tubes. — We observe 

 in the various descriptive catalogues of American Microscopes, that 



* Amer. Journ. Micr., v. (1880) p. 185. 



