On the Light/ron incombujlible Bodies. 517 



Mr. T. Wedgwood found that fluor fpar, phofphate of lime, flint, &c. were luminous, 

 not only when heated, but when ftruck together, and that under water, or in any kind of 

 air. Scheele difcovered that fluor fpar, after calcination, loft its phofphorefcence. I ex- 

 pofed to a long continued red heat fluor fpar, phofphate of lime, fulphate^of ftrontian, 

 fulphate of barytes, glafs, fulphate of lime, and carbonate of lime, all of which were before 

 phofphorefcent, and produced light by collifion under water. 



After being fufl^ered to cool in the light, they were placed on a heated iron fucccflively. 

 The fluor fpar, the phofphate of lime, and the fulphate of ftrontian and barytes, were not 

 phofphoric at any temperature. The calcareous fpar, which had loft a portion of its car- 

 bonic acid, and the gypfum, were nearly as luminous as before ; the phofphorefcence of the 

 glftfs and flint was barely perceptible. 



Two pieces of the calcined fluor were now rubbed together, they produced as much light 

 as before. The phofphate of lime, the calcareous fpar, and the gypfum, had loft their 

 coherence ; fo that the pieces could not be rubbed againft each other with fufficient force. 

 The fulphate of ftrontian and barytes, the glafs, and the filex, produced as much light at 

 before on collifion. 



I found that all thefe bodies were non-condu£iors of eleftric fluid. On rubbing a large 

 cryftal of quartz with woollen, it became highly eledlric. Fluor fpar was likewife made 

 ele£tric when heated and ftrongly rubbed. To prove, however, more fatisfa£lorily 

 whether the light produced by the collifion of two non-condu£lors was eledtric, two 

 cylinders of glafs were ftruck againft each other, fo as to produce light, and one of them 

 was placed in contaft with a Leyden phial. After a nuhiber of coUifions, on applying a 

 conductor to the phial, I procured a fmall fpark. 



Two pieces of pyrites, fufHciently hard to cut glafs, and extremely brittle, produced an 

 immenfe quantity of light, when ftruck together, in the atmofphere -, but not tlie flighteft 

 luminous appearance under water. This body is a good conductor of eleftric fluid. 

 Do not thefe fa£ls go far to prove that light, when produced by the collifion of bodies in 

 water, or non-refpirable air, is eleftric ; and generated by the rapid tranfmiflion of ele£lri- 

 cal fluid, excited by collifion between two non-condu£ting furfaces, to a condudling body ? 

 And as iron can be heated, to a degree at which it is capable of decompofing oxigene gas, in 

 a non-refpirable air without being luminous ; and as pyrites is not luminous under water, 

 is it not probable that light is accidental to, and not neceflarily produced by, high tem- 

 perature? 



The admiflion of fuch inferences would be favourable to my theory of the combinations 

 of light ; but fadts have occurred to me witii regard to the decompofition of bodies which I 

 have fuppofed to contain light, without any luminous appearance. Till I have fatisfaftorily 

 explained thefe fafts by new experiments, I beg to be confidered as a fccptic with regard to 

 my own particular theory of the combinations of light and theories of light in general. On 

 account of this fcepticifm, and for other reafons, I fliall in future ufe the common nomen- 

 clature; excepting tliat as my difcoveries concerning the gafeous oxide would render it.higUy 



Vol. III.— February 1800. 3X improper 



