ELEMENTARY PHOTO-MICROGRAPHY. 55 



brilliant tints that before were absolutely in- 

 visible. Next try the crystal with dark-ground 

 illumination. Here again it presents a fascinating 

 sight like a flashing jewel on black velvet. Either 

 a spot lens or a central stop in the condenser may 

 be used for the purpose, or even swinging the 

 mirror to one side and throwing oblique light will 

 give the effect. Further, the object may be put 

 under reflected light, when again it presents a 

 totally different appearance. 



Next a combination of reflected light and 

 transmitted light may be tried, which will have 

 the effect of making the crystal stand out in relief, 

 and offer noteworthy points. After all these, the 

 microscopist is not at the end of his resources. 

 He may then insert colour discs in the condenser, 

 and have the crystal one colour with a background 

 of any other colour he pleases. 



Of course, not every object will allow of every 

 kind of lighting, but most will stand two or three. 



Other advantages probably may be obtained 

 by the use of colour screens or light filters. From 

 the foregoing remarks, then, it will be gathered 

 that the landscape photographer has no power 

 to alter the prevailing light and shade, whilst the 

 photo-micrographer can modify them at pleasure. 

 But, on the other hand, the latter will find diffi- 

 culty in getting any contrast at all when dealing 

 with very transparent objects, and it is here that 



