80 THE AMERICAN MONTHLY [Mch 



Crystals. — The forms of microscopic crystals may be 

 accurately reproduced on glass by etching with fluoric 

 acid. Interesting and beautiful effects may be obtained 

 by crystallizing various salts in a thin layer on a glass 

 slip which has been well warmed to prevent the crystals 

 from dissolving, and then exposing the glass to the ac- 

 tion of the vapor of fluoric acid for three or five minutes. 



Insects, — Many Aphides and Coccids are covered wit 

 a waxy secretion which interferes very materially with 

 their easy examination. To remove this waxy secretion 

 place the insect on a piece of platinum foil and pass it 

 once over the flame of the alcohol lamp. The wax melts 

 at a surprisingly low temperature, and leaves the insect 

 perfectly clean for study. This method i.-^ particularly 

 useful in the removal of the waxy cocoon of the pupa? of 

 male Coccidse, and is quicker and more thorough than the 

 use of any of the chemical wax solvents which have been 

 suggested. 



Objectives. — Oil-immersion objectives require much 

 care in use. A small quantity only of the fluid should be 

 employed, and then wiped off as soon as possible when 

 finished with. The removal of the prepared cedar oil, 

 which is generally used, should be effected with blotting 

 paper, and the lens cleaned by first breathing on it and 

 afterwards wiping lightly with a piece of clean, soft linen. 

 To keep the immersion fluid unchanged it ought not to be 

 exposed to the air for any length of time, as free access 

 of air results in thickening and consequent alteration of 

 the refractive index. 



A Tele-microscope. — A kind of combination telescope 

 and microscope has been worked out by a French micros- 

 copist for studying live insects and their habits. The new 

 apparatus is called the "telemicroscope," and is really 

 a small telescope having an objective formed of two 

 achrom;;iic lenses, which can be moved nearer together 



