ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 363 



covery of the conjoint use of the vertical illuminator with American 

 immersion objectives of wide balsam apertures.* By way of demon- 

 stration, Mr. Morehouse exhibited the Podura scale under amplifica- 

 tions of 4000 diameters, as well as other objects. 



" Thus it appears that until five years ago there was no known 

 means of working high powers with reflected light, and when we 

 remember that the vertical illuminator proved to be a difficult instru- 

 ment in the hands of one not expert either in its use or that of the 

 wide-apertured objectives — that probably 50 per cent, of those who 

 have made the attempt have failed to use it successfully — the reasons 

 become apparent lohy so little has been accomplished in this direction. 



" This is a natural field of Microscope investigation ; we thus see 

 things through the Microscope as we see them day after day with the 

 naked eye, namely, by light reflected from the surface. It often thus 

 occurs that such eye examinations of the surface suggest the pro- 

 priety of dissecting the object into smaller and smaller parts, so that 

 the object may be further inspected in detail. The same holds good 

 when it is under the objective and vertically illuminated. 



" The wider the balsam aperture of the immersion objective the 

 better its conjoint work with the vertical illuminator. Here we have 

 additional evidence of the value of wide apertures. 



" Under the vertical illuminator the dry valves of S. gemma sur- 

 render their true structure. It will be seen that these shells are 

 enveloped in an exceedingly thin membrane, which, in most cases, is 

 ruptured, or torn from certain portions of the shell, and that it is 

 only through the opening thus formed that the underlying 'markings' 

 are truly seen. If the same valve be viewed by transmitted light the 

 image will be shown falsely owing to the illumination." 



I See the next note as to this not being " opaque " illumination.] 



AmpMpleura pellucida by Reflected and Transmitted Lig^ht. 

 — At the ordinary meeting of the Society on 10th November, 1880, 

 Mr. T. Powell, jun., exhibited A. pellucida (dry on cover-glass) in a 

 somewhat novel manner — illuminated from above and below at the 

 same time. 



With one lamp placed at the side, the light was reflected by the 

 vertical illuminator upon the posterior surface of the objective, and 

 thence condensed upon the object, the lens acting as the condenser 

 for the illumination and as object-glass at the same time. By the 

 adjustment of a side diaphragm applied to the vertical illuminator, 

 and by rotating the object into the required position, this illumination 

 developed an appearance of " dotted " superficial structure. Another 

 lamp was used to direct a pencil through the ordinary achromatic- 

 condenser of Powell and Lealand. By the slot diaphragm trans- 

 mitting a small pencil refracted very obliquely through the margin of 

 the condenser, this illumination exhibited the usual transverse striae. 

 A screen was arranged to cut oif the illumination from either lamp, 

 so that the object could be seen by either illumination successively. 



The object was viewed by the new y'^ oil-immersion (with cor- 



* See this Journal, ii. (1879) p. 194. 



