380 History of Luminescence 



evidenced by the careful experiments of Robert Boyle, made on 

 October 27, 1663, and reported to a meeting of the Royal Society 

 next day.^ Boyle's particular diamond " that shines in the dark " 

 belonged to a Mr. Clayton, whereas most of his own diamonds as 

 well as rubies, sapphires, and emeralds did not exhibit this property. 

 The stone was hard and would write on quartz but was dull in 

 appearance and blemished with a whitish cloud in the middle.* 

 Boyle found " this to have like other diamonds an electrical faculty," 

 as indicated by the attraction of light objects. " Being rubbed upon 

 my clothes as is usual for the exciting of amber, wax and other elec- 

 trical bodies, it did in the dark manifestly shine like rotten wood, 

 or the scales of whitings or other putrified fish." Holding the dia- 

 mond near a candle made it shine in the dark, although less inten- 

 sely, and it did not then become electrified, whereas holding it over 

 a well heated but not glowing piece of iron made it glow only 

 slightly. 



The last experiment would seem to indicate Mr. Clayton's dia- 

 mond was weakly thermoluminescent, and the candle experiment 

 would indicate phosphorescence.^ Boyle sho^ved that the diamond, 

 previously excited by rubbing on cloth, would luminesce under 

 water and other liquids, but it could not be excited if rubbed while 

 under water or with a damp cloth. Evidently electrification of the 

 diamond played some part in its glowing. It seems probable that 

 the light of electroluminescence, as well as the light of the candle 

 excited the phosphorescence of the diamond, which then lasted 

 some time. 



Boyle went on to demonstrate that " incalescence " had little to 

 do with the glow in rubbing but that " compression of its parts " 

 was an important factor. By pressing on one spot (without rub- 

 bing) with a Avell-glazed white tile or with a steel bodkin, there was 

 disclosed " a very vivid but exceedingly short lived splendor, not to 

 call it a little coruscation." This last experiment would appear to 

 demonstrate true triboluminescence, i. e., piezoluminescence, of the 

 crystal. Even though Boyle did not separate the various types of 

 luminescence, his communication is a model of experimental pro- 

 cedure, and deserves to be read by all interested in the history of 

 science. Boyle's observations on the diamond were repeated by 



"T. Birch, Works of Boyle 1: 796-799, 2nd ed., 1772. Publication of the Phil. Trans. 

 did not begin until March 6, 1665. The account was annexed to Experiments and 

 considerations touching colours (London, 1664) , see figure 37. 



* Boyle later showed that some clear diamonds would also glow after rubbing. He 

 tried to buy Clayton's diamond, but Clayton would not sell. 



^ Had the diamond been exposed to sunlight and then wanned in the dark, thermo- 

 luminescence might have been marked, but Boyle did not perform this experiment. 



