1893.] THE MICROSCOPE. 13 



PRACTICAL SUGGESTIONS. 



Light. — The best light to use for microscopic work is day- 

 light, and the best daylight comes from a uniform gray cloud. 

 A pure blue sky does not give the fullest power to a high 

 objective. Avoid quickly passing clouds and direct sunlight. 

 Set the microscope six or eight feet from the window. 



Arithmetical Microscopy. — The best book on the theory 

 and mathematics of the microscpe is Naegeli and Schwendener's 

 Microscope in Theory and Practice, an English edition of which 

 has been published by Macmillan & Co., New York. Most of 

 it is too abstruse for any but professional microscopists. 



The Eyes. — A friend of ours recently forbid his son to use 

 the microscope because the young man's eyes were not strong, 

 and further injury was feared. But with care one may learn to 

 use the eyes a large amount without injury. Do not use a micro- 

 scope for an hour after eating, nor in the early morning. Alter- 

 nate the use of the eyes and habituate both to the use of the tube. 

 Always discontinue work when the eves show signs of fatigue. 



Injuries to the Microscope. — If chloride of calcium and 

 nitric acid, fuming hydrocloric acid, etc., are placed, when 

 heated, close to the microscope the lacquer will be injured 

 thereby. Similarly, sulphureted hydrogen, volatile acids, 

 chlorine, and many gases developed in chemical operations will 

 attack the instrument. For many reasons the instrument should 

 be kept under cover as much as possible. 



Cutting. — Before cutting a section, moisten both the blade 

 and the object in order to secure a smoother and more natural sur- 

 face. Draw the knife as if it were a saw, and do not push it as 

 if it were a chisel. Thin and troublesome objects may be 

 allowed to solidify in gum or paraffin. They may sometimes be 

 cut between elder-pith or cork. 



Good Permanent Paste. — A strong paste that will keep for 

 a year or longer may be made in this way : After dissolving 

 one teaspoonful of alum in one quart of water, stir in as much 

 flour as will give it the consistence of thick cream, being par- 

 ticular to break up the lumps ; stir in as much powdered resin 

 as will lie on a dime, and a half dozen cloves. Have on the fire 

 a saucepan with a teacup of boiling water ; pour the flour mixture 

 into it, stirring well all the time. In a few minutes it will be of 

 the consistence of porridge. Pour it into a jar, let it cool, and 

 tie over, putting it into a cool place. When any is needed, take 

 out a portion and soften with warm water. Its keeping qualities 

 will be enhanced by the addition of five grains of hydronaphthol 

 dissolved in a little alcohol. 



