ELEMENTARY PHOTO-MICROGRAPHY. 53 



familiarity of one special illuminant be acquired, 

 and results be tabulated for ready reference. 



The man who is always changing his methods 

 is not as a rule either able to satisfy himself or 

 to produce a creditable output ; therefore, it is 

 not advisable to try every kind of light and every 

 brand of plates or paper before settling down to 

 steady work. 



In selecting a radiant, the chief thing to be 

 considered is that the light shall be steady and of 

 the same illuminating effect at all times. The 

 length of exposure may be shortened or lengthened 

 by using a more or less intense light, always 

 remembering that the more intense the light the 

 more the trouble from heat and other dangers. 



Theoretically the source of light should be a 

 mere point, and consequently of great brilliancy ; 

 but for very transparent objects a less luminous 

 source is even an advantage. Bearing these con- 

 ditions in mind, the reader may decide according 

 to the circumstances of his environment which 

 lamp to adopt. If electricity be available, this 

 offers everything necessary. Limelight is good 

 but troublesome. Acetylene gas is easily worked 

 and satisfactory. Incandescent gas or a well-made 

 incandescent spirit lamp with inverted mantle is 

 convenient and powerful. 



Magnesium wire answers well for short expo- 

 sures, and instantaneous photographs may be 



