MI.M..III VIII.] THE PHOSPHORESCENCE OF BODIES. 



tnry exposure to the sun. He also investigated how far 

 tin glow was connected with electrical relations, and 

 showed its perfect independence. He also greatly in- 

 creased the list of phosphori, asserting that, so far from 

 the quality being a peculiarity of the Bolognian stone, 

 Baldwin's compound, the diamond, all solid substances 

 except the metals, are phosphorescent when rightly treat- 

 ed, and even these he believed would eventually be 

 found to have the same property. 



There is one point upon which Du Fay dwells that 

 deserves more than a passing remark the connection 

 between phosphorescence and temperature. He proved 

 that phosphori cannot absorb light so well when they 

 are warm as when they are cold, and that a rise of tem- 

 perature always makes them disengage their light. 



It is obvious that these early investigators labored 

 under great difficulties arising from the imperfect chem- 

 ical science of those times. They confounded together 

 things that were essentially different, such as the shining 

 of urine-phosphorus with the glow of the diamond, and 

 this again with the electrical light arising when friction 

 has been employed. Then, again, their erroneous views 

 of the composition of bodies were constantly leading 

 them astray. Thus Du Fay, finding that the Bolognian 

 stone (barium sulphate) emitted a sulphury smell, and 

 thinking that it shone because of the burning of the 



o o 



sulphur, transferred the same explanation to the case of 

 yellow diamonds, and asserted that they also glowed 

 through the combustion of the sulphur that discolored 

 them. 



I do not intend now to give a review of the subse- 

 quent discoveries and hypotheses brought forward by 

 the numerous experimenters of the last century, or by 

 Heinrich, the Becquerels, Biot, Poggendorff, Pearsall, and 

 many others in this. I may, however, recall attention to 



