The Eighteenth Century 153 



and transpiration produced an effect similar to fermentation. Part 

 of the light-giving sulphur which they contain thereby collected in 

 vesicles or was filtered in purifying glands, from which it escaped 

 because of its abundance and extreme agitation. 



Mercury was regarded as a material in which the light substance 

 was already present but so rare and weak that it did not appear 

 unless the air was removed from it (as in a barometric vacuum) 

 and it was gently agitated. The diamond was a material in which 

 the sulphur had need of excitation by violent rubbing. 



All artificial phosphores had passed through fire and their sulphur 

 had consequently received various modifications, i. e., their sulphur 

 had been released and augmented. Fire itself was thought to be 

 made up of foreign corpuscles with a great quantity of sulphur, all 

 luminous. In preparation of phosphores, fire moulded the pores of 

 the material into a " figure " convenient to receive the corpuscles 

 of light. 



De Mairan explained why the " phosphore brulant " of Kunkel 

 could not be made as readily from urine after wine drinking as after 

 beer drinking. Like Lemery, he held it was owing to the fact that 

 the sulphur of wine was " beaucoup plus exaltez " than that of beer 

 and dissipated itself more during fermentation or in the fire neces- 

 sary for preparation. Kunkel's phosphorus contained, in addition 

 to sulphur, much saline principle to ignite the material, which 

 required air or humidity, and should be sprinkled with some 

 " licqueur " which causes a subtle and violent fermentation called 

 an effervescence. The light of burning phosphorus was said to be 

 as bright as sunlight gathered into focus by a silver mirror. 



These explanations certainly represent a valiant attempt to bring 

 together a number of diverse (unfortunately too diverse) phe- 

 nomena and to explain them by a common principle. It will be 

 noted that de Mairan was greatly influenced by Lemery and his 

 phrase, " agitation of insensible parts," as the mechanism of light 

 production. He spoke of sulphur as the particles which become 

 agitated and the material which explains everything. Although 

 Lemery is not mentioned in the essay, in fact there are no refer- 

 ences, certain passages very clearly indicate that Lemery's work had 

 been carefully read. The essay ended with a quotation from Pliny: 

 " Often contemplating the nature of things, I am persuaded to think 

 nothing is incredible." 



De Mairan was born at Beziers, near Montpellier, but removed 

 to Paris in 1718, when he was elected a member of the French 

 Academy. He was not only a scientist interested in many subjects, 

 especially in celestial and meterological phenomena, but a littera- 



