196 THE AMERICAN MONTHLY [June 



objections made to artificial light have arisen from its im- 

 proper employment. The main requirements in the light 

 are simplicity and ease of manipulation. These com- 

 bined with proper adjustment will give an effective light. 

 The electric light, the oxyhydrogen light, the magnesium 

 light, gas light, oil light, and, latest, acetylene light, have 

 all been employed for photomicrographic purposes. The 

 electric, oxyhydrogen, and magnesium lights all require 

 rather complex apparatus, and they are all open to this 

 objection, together with certain other objections pertain- 

 ing to each. Of the magnesium light it may be said that 

 no practical apparatus for its production has been de- 

 vised. Electric light necessitates connection with an 

 electric plant. It is expensive and the apparatus required 

 is complicated. In the form of the arc light it gives a 

 very satisfactory and powerful light, and it is probably 

 the best form of artificial light for large institutions 

 when used in the manner hereafter described for oil and 

 acetylene light and with heat filter added. Aside from 

 its power, second only to sunlight, it possesses no advan- 

 tage over cheaper and more easily handled lights. The 

 oxyhydrogen light is expensive and is troublesome to 

 manage. It requires a complicated apparatus and does 

 not give a light of sufficiently greater power over oil, gas, 

 or acetylene to compensate for the trouble involved in its 

 management. 



For practical work there remain, therefore, oil, gas, 

 and acetylene light. These are all easy to manage, they 

 are best used in a similar manner, with similar apparatus, 

 and for advantages of cheapness, steadiness, and con- 

 trollability are unsurpassed. They differ in illuminating 

 and actinic power, oil light being lowest, and acetylene 

 light highest. Oil and gas light are of very nearly equal 

 power, but they have not generally been considered 

 powerful enough except for low and medium powers. 



