MKMOIR VIII.] THE PHOSPHORESCENCE OF BODIES. 



water, b the pressure screw, c the phosphores- 

 cent spar or substance. 



These experiments have a bearing on Le- 

 mery's theory. A mass of iron suddenly com- 

 pressed grows hot; so, too, does atmospheric 

 air. It would, therefore, not be unreasonable 

 to expect that if a phosphorus acted like a 

 sponge to light, and were thus pressed upon, 

 it would yield up its light. But conceptions 

 derived from the old theories of specific heat r Fig . 15 1 

 are perhaps scarcely applicable here. 



When unequal pressure is applied, the result is differ- 

 ent. A piece of chlorophane pressed by a forceps glows 

 brightly; if crushed, the fragments sparkle like little 

 fire-works as they fly through the air. If the spar be 

 previously powdered, a shining is still produced, and 

 when the pulverization is conducted in an agate mortar 

 in the dark, bright eddies of light follow the track of 

 the pestle. In these cases, however, the separation of 

 the laminae of the crystal and the heat produced by 

 friction probably determine the result. Canton's phos- 

 phorus did not shine when compressed or submitted to 

 friction. 



2. Does any structural change accompany the phos- 

 phorescence of bodies? 



The foregoing experiments appearing to prove that 

 if there be any expansion of a phosphorescing body, it 

 is to a very small amount, I next endeavored to de- 

 termine whether there is any molecular change, or new 

 structural arrangement, which can be detected by polar- 

 ized light. 



A flat piece of fluor-spar, polished on both sides, was 

 placed in a polariscope, and a pair of blunt iron wires 

 connected with a Leyden-jar were adjusted near the 



K 



