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POPULAR SCIENCE MONTHLY. 



the object in general obtains when the Abbe condenser is as far away 

 from the microscopic slide on one side as is the objective on the other. 

 Thus for oil immersion work a drop of oil must be placed between the 

 condenser and slide as well as upon the objective. It frequently happens 

 that when the proper position of the condenser is located for low power 

 objectives the detail is somewhat obliterated because of too intense 

 illumination, and the manipulation of the iris diaphragm connected 

 with the condenser is necessary in order to obtain the best results. 



From whatever source the light falls upon the Abbe condenser, an 

 auxiliary condenser before it is advantageous, except when daylight is 

 used upon the mirror beneath the stage. The use of daylight has disad- 

 vantages, however, which do not recommend it for photographic work. 

 With diffused light falling upon the mirror it is impossible to use even 

 moderately high power objectives and obtain sufficient light for focus- 



Fig. 1. Convenient Arrangement of Apparatus for Ordinary Photomicrographic 



Work. 



ing, while with the direct rays of the sun, unless a heliostat is used 

 to maintain the position of the sun constant upon the mirror, one cannot 

 obtain a photograph before the sun has changed enough to throw the 

 image of the object off the plate. In addition to this inconvenience in 

 general, the optical imperfections of the mirror are such as to make 

 the production of sharp photographs difficult, and much better results 

 are obtained with high magnifying power, by dispensing with its use 

 and transmitting the light directly from the source through the optical 

 system. 



Photomicrographic work of low magnification has been successfully 

 done with the various forms of artificial illuminants of low candle 

 power. The writer, in the production of first photographs used very 



