196 FIRESIDE SCIENCE. 



light, in passing through, is refracted in a way to 

 produce a maximum of brilliancy. The rough gems 

 are quite dull or lustreless, and it requires consum- 

 mate skill in cutting and polishing to secure the ac- 

 curacy of angular proportion in the faces necessary 

 to perfect results. There must be principal planes 

 or faces, and around them a considerable number of 

 smaller ones, all placed at correct angles, so that, 

 by refraction, a blaze of light, every ray in harmony, 

 may be the result. The skill of the operator is 

 shown in his ability to bring out the whole power of 

 a stone. 



The diamond is the hardest of known substances, 

 and hence the inquiry will naturally arise, " How is 

 it possible to produce mechanical effects upon a sub- 

 stance so refractory ?" "Diamond cut diamond" 

 is an old adage, and it has a practical illustration in 

 the factory. The dust of the gem is employed to 

 wear away the surface of those undergoing the pro- 

 cess of polishing, and this is obtained by grinding 

 worthless particles in a steel mortar, and also the 

 minute fragments obtained in the progress of the 

 work are saved for the purpose. But these two 

 sources of supply do not afford sufficient material to 

 meet the wants of the industry, and consequently a 

 substance found in association with diamond, and 

 possessing equal hardness, is to a large extent 

 employed. This pebble, which has no value as a 



