20 4 THE MICROSCOPE. 



ber and front cell was protected from the light by the piece of rub- 

 ber,, but, notwithstanding all this, the resolution was as good as 

 before! 



A few days ago I blacked the front cell of a Spencer -fe with 

 Chinese ink, and then getting the fluid into the position described 

 by Dr. Detmers as most favorable, I tried to effect a resolution; but 

 although the blacked surface radiated some light it was not suffi- 

 ciently intense to enable amphipleura pellucida to be resolved! 



I then took a piece of tin foil about an inch square and made a 

 hole in it whose diameter, although slightly smaller than that of the 

 front lens, was a little larger than its working diameter. This was 

 placed upon the cover-glass and pressed down until the fluid ex- 

 tended to nearly the edge of the tin foil, the fluid being between the 

 cover and tin foil. The hole in the foil was brought over the diatom 

 and after applying a little more fluid above the foil the objective was 

 lowered. The resolution was as good as before and the light was 

 very white. 



I have now presented a series of facts which substantiates my 

 explanation as given in the June issue, and which shows the incor- 

 rectness of Dr. Detmers' theory. In fact, I have shown that while 

 his theory is "untenable and contrary to all optic laws," my own is 

 in perfect accordance with every law governing the reflection of 

 light under similar circumstances. 



I am surprised to learn that Dr. Detmers should regard the evi- 

 dence of color correction as "mere bosh" in regard to central or 

 • oblique light, and as he has made the statement that it is so, I 

 should like to have him explain why it is so, and I will endeavor to 

 prove the incorrectness of that supposition also. 



PRACTICAL HELPS. 



BY E. H. GRIFFITH. 



THE following may be of interest and of value to some of the 

 readers of the Microscope: 



RINGING SLIDES. 



Delicate colored circles may be made with a pen and aniline 

 inks on slides finished with white zinc. Center the slides on a turn- 

 table and hold the pen in the same manner that a brush should be 

 held. 



