LUMINOUS DIAMONDS 27 



light. The most wonderful, however, in this respect are 

 the rare diamonds which become luminous merely by 

 rubbing, and leave phosphorescent streaks on the cloth 

 with which they are rubbed. This property is similar 

 to the phosphorescence shown by other kinds of crystals 

 when heated or when simply fractured. 



Diamonds are readily distinguished from paste by the 

 Rontgen rays, since they are transparent to those rays, 

 whilst paste (or glass) is opaque to them. Radium also 

 causes diamonds, but not paste, to phosphoresce. All 

 diamonds are not equally hard, though they are the 

 hardest of stones, and harder than steel, but not harder 

 than the metal tantalum. Some Australian diamonds 

 are known (from Inverel, New South Wales) which are 

 so hard that at one time they could not be cut and 

 polished ; but only four years ago the rapidity of the 

 wheels used in these processes was greatly increased, and 

 these terribly hard diamonds were brought into subjec- 

 tion. 



Thus it is clear that there are many extraordinary 

 features of interest about the diamond, and that its 

 brilliance and high price constitute only a small part of 

 its fascination. 



10. Science and Fisheries 



Science, the knowledge of the vast system of orderly, 

 inexorable activities under which we exist, and of which 

 we, and all that we can apprehend, are but more or less 

 significant parts, is not only to be regarded as a gratifica- 

 tion of our curiosity, as food for our imagination, and 

 the basis of our philosophical theories. It is, in addition 

 to these, a thing of unparalleled importance to the 

 immediate daily welfare of every man, woman, and 

 child, and upon its due cultivation and use depend the 

 future welfare, even the existence, of whole races of 



