1897J MICROSCOPICAL JOURNAL. 157 



The difference, m minus n equals a and equals depth of 

 cell filled with air. 



In like nianner a drop of the liquid whose index of re- 

 fraction is to be determined, is placed in the cell and the 

 cover applied as before and pressed down with the finger. 

 Let us suppose it is water, and that the equation for air 

 substituted is 30 microns minus 20 microns ec^ual 10 mi- 

 crons, or the depth of the cell filled with air. A equals 

 10 microns. 



Now, m minus n equals b and equals depth of cell filled 

 with water. Substituted we have 27.5 microns minus 7.5 

 microns. B equals 7.5 microns. A divided by b equals 

 10 divided by 7.5 which equals 1.833 the index of refrac- 

 tion of water. 



For obtaining' the index of transparent solids with 

 plain sides, as for instance of cover glasses or slips, the 

 apparent depth is obtained as before, the real thickness 

 measured with the cover glass guage or calipers. Their 

 ratio is the index. 



It is not within the province of this article to suggest 

 the important or varied applications attendant on the 

 determination of this index, but the writer will feel 

 highly repaid if it is of interest to any of the readers of 

 the Journal. 



EDITORIAL. 



Prof. Edson S. Bastin.— The death of Prof. Edson S. 

 Bastin means a severe loss to the body of American scien- 

 tists. He was one of the most faithful workers in pharm- 

 acy. For the last two years he has devoted himself so 

 unceasing-ly to microscopical work outside of the hours 

 devoted to instruction, that he has virtually allowed him- 

 self no proper time for rest, and as a matter of fact, has 

 almost worked himself to death. His work on the anatomy 

 of plants of the pine family has been recog-nized as of great 

 importance here and abroad. 



