54 ELEMENTARY PHOTO-MICROGRAPHY. 



taken by flashlight. Authorities differ very widely 

 about paraffin oil. Some condemn it altogether ; 

 but in the writer's opinion a good oil lamp is the 

 most convenient and best for anyone who has to 

 work at intermittent and irregular times. It can 

 be started at any moment without preparation, 

 and will perform excellently whether high powers 

 or low powers be employed. In fact, negatives 

 from the most difficult test objects can be secured 

 that will compare favourably with those taken 

 by any of the lamps previously named. 



Assuming that preference is shown for one of 

 the lamps just named, the next desirable thing is 

 to use it under different conditions. So many 

 people fail to take advantage of the varied methods 

 of illuminating an object under view that much of 

 the usefulness of a microscope is lost, and the 

 owner fails to grasp the immense possibilities of 

 other systems than the one to which he confines 

 himself. For instance, take a simple transparent 

 crystal with polarising properties, and view it 

 under direct or transmitted light. Its configura- 

 tion is certainly visible, but no adequate con- 

 ception of its inherent beauty can be got from 

 such inspection. Now add a polariscope to the 

 microscope, and what was merely as uninteresting 

 as a piece of plain glass becomes arrayed in gor- 

 geous colours, ever varying in beauty as the prism 

 is rotated on its axis. Parts are differentiated in 



