176 THE BOOK OF THE LANTERN. 



figures, and he made many experiments in this direction. 

 He found that almost all the common oils and fats give 

 natural diagrams by which they can be identified ; and 

 further, that these figures will vary, according to the length 

 of time for which the oil has been exposed to the air. To 

 get some idea of the nature of these beautiful figures, a 

 drop of pure sperm oil may be allowed to fall on the surface 

 of a pan of water. It will be seen in a few seconds that 

 the film of oil will break up into a number of little open- 

 ings, and that it will exhibit a pattern of great beauty. 

 Rape oil, Lucca oil, and some others, give patterns of en- 

 tirely different designs ; some of them very much resembling 

 beautiful crochet- work. In order to show these patterns 

 in the lantern, we have two or three different methods of 

 going to work. We can exhibit these cohesion figures, for 

 instance, by the simple aid of two pieces of clear glass. 

 Between two such plates put a little vaseline, which in 

 order to increase the effect on the screen may be coloured 

 red with alkanet root. The plates are pressed together, with 

 the vaseline between them, and are then secured by a ring of 

 india-rubber at each end. They are then put into the lan- 

 tern, and while standing upon the lantern stage the blade 

 of a knife is inserted between the two glasses and gradually 

 turned so that they are slightly separated. The effect 

 upon the screen is very beautiful, the disc appearing to be 

 covered with arborescent figures. This experiment may be 

 repeated more than once, but the vaseline will require 

 renewal after a time. Another mode, and perhaps a better 

 one, of showing the same phenomena, is by means of the 

 vertical attachment to the lantern. In this case the 



