1893.] THE MICROSCOPE. 63 



146. Where can prepared sections of bone be procured? 



-j. 1. p. 



The dealers in microscopical preparations will supply such 

 mounts. 



147. An accidental pressure upo?i the cover-glasses of some 

 mounts caused the medium to exude, a?id the covers slip down 

 when the slide is placed on edge. What were the defects in 

 mounting? — E. L. S. 



Many mediums remain soft under the cover. All such mounts 

 should be protected with a finish of good tough varnish around 

 the edge of the cover. 



148. — How may I compute the magnification of an object 

 photographed with or without an eyepiece, and at diferent 

 distances from the objective? — A Novice. 



The easiest way to find this magnification is to remove the 

 object after photographing it, put a stage micrometer in its place, 

 throw the image of the lines on the ground glass, and compare 

 them with an ordinary rule. This will give the correct magni- 

 fication produced by that optical combination. To compute it 

 more or less accurately, reckon that an inch objective will amplify 

 10 diameters at to inches from its optical centre. If an inch eve- 

 piece is used, multiply again by 10 ; other objectives, eyepieces, 

 and distances in proportion. 



DO 



AB 



of eyepiece. B = focus of objective. O = optical tube length 

 (from optical centres). D = distance from object to eye or 

 ground glass. As eyepieces and objectives are rarely rated cor- 

 rectly, computation by any rule will give approximate results only. 

 See A. M. M.J., vol. vi, page 141. 



Nelson's formula is, - K n = magnification. A = focal rating 



SCIENCE-GOSSIP. 



Specific Stains. — Carmine, hematoxylin, and most of the 

 anilin dyes stain unaltered cellulose, whilst lignified tissue may 

 be permanently stained with methyl-green (0.25 gram in 20 c. c. 

 of alcohol and So c. c. of distilled water). Squire's process for 

 double staining stem and root sections containing cellulose and 

 lignified tissue is to first rinse in distilled water, then place in 

 methyl-green solution for 3 or 4 minutes ; again rinse in water, 

 wash in 90 per cent, alcohol for 5 or 10 minutes, place in 

 Grenadier's alcoholic borax carmine for 15 or 20 minutes, rinse 

 quickly in water, and pass through 90 per cent, alcohol. Chlor- 

 zine iodine colors cellulose blue, and lignin yellow or yellowish 



