50 "N" RAYS 



to this may doubtless be ascribed the fact that 

 they have remained so long undetected. 



I was then led to ask myself whether bodies 

 which are themselves in a state of strained 

 internal equilibrium would not emit " N " 

 rays. That they do so is indeed 'confirmed by 

 experiment. Rupert's drops, hardened steel, 

 hammer-hardened brass, melted sulphur of 

 crystalline structure, etc., are spontaneous and 

 permanent sources of " N " rays. One can, for 

 instance, repeat the experiments with the clock 

 dial, employing, instead of a compressed body, 

 a hardened steel tool, such as a chisel or file, or 

 even a pocket-knife, without in any way bending 

 or compressing them ; similarly, bringing near 

 to a small mass of phosphorescent calcium 

 sulphide a knife-blade or bit of unannealed 

 glass is sufficient to increase the phosphor- 

 escence. Non-hardened steel is without action ; 

 a chisel which is successively hardened and 

 softened in turn is active when hard and in- 

 active when the temper is taken out of it. 

 These actions traverse, without any notable 

 weakening, a plate of aluminium i "5 cm. thick, 

 an oak board 3 cms. thick, black paper, etc. 



