52 



COHESION. 



sealing-wax which I have put there. The 

 light which now goes to you from that piece of 

 silver was obstructed by the edge of the basin, 

 when there was no water there, and you were 

 unable to see anything of it ; but when we 

 poured in water, the rays were attracted down 

 by it, over the edge of the basin, and you were 

 thus enabled to see the articles at the bottom. 



I have shown you this experiment first, so 

 that you might understand how glass attracts 

 light, and might then see how other substances, 

 like rock-salt and calcareous spar, mica, and 

 other stones, would affect the light; and, if 

 Dr. Tyndall will be good enough to let us use 

 his light again, we will first of all show you 

 how it may be bent by a piece of glass (fig. 19). 



Fig. 19. 



[The electric lamp was again lit, and the beam 

 of parallel rays of light, which it emitted, was 



