The Eighteenth Century 175 



, . . Heat is a Motion in the Particles of a Body with a lesser Degree of 

 Velocity; and Fire a Motion with a greater Degree of Velocity, viz. such 

 as is sufficient to make the Particles shine, though we often call such a 

 Degree of Heat as will burn. Fire, though it does not actually shine; 

 and we seldom call those lucid Bodies Fires which only shine and do not 

 burn. These are a Sort of Phosphori, which though they have no Heat 

 yet seem to owe their Lucidity to the Motion of the Parts. 



This I think will appear for the following Reasons; (1) We observe 

 several of those Phosphori are owing to Putrefaction, as rotten Wood, 

 very stale Meat, especially Veal, some Sort of Fish long kept, as Oysters, 

 Lobsters, Flounders, Whitings, etc. which Putrefaction is the Effect of a 

 slow and gentle Fermentation, and that consists in the Intestine Motion 

 of the Parts, as we have formerly shewn. (2) Most of those Phosphori 

 have their Light so very weak as to shine only in the Dark, which seems 

 to indicate a lesser Degree of Velocity in the Parts than what is necessary 

 to Produce Heat; for such a Degree of Velocity will cause Bodies to shine 

 in open Day-light. (3) Some of those Noctiliicae, or Bodies which shine 

 in the dark, are the Parts of animated Bodies, as in the Glow-Worm, a 

 small Sort of Centipede, etc. but all the Parts of an Animal are undoubt- 

 edly in Motion. (4) Other Phosphori put on the Appearance of Flame, 

 as the Igi-iis Fatuiis, the Writing of common Phosphorus made from 

 Urine, Flashes of Lightning, etc. but all Flame is nothing but a kindled 

 Vapour, whose Parts are all in Motion, but may be too weak to cause 

 Burning. (5) Several of those innocent lambent Flames may have their 

 Matter so agitated, or the Velocity of their Motion so increased, as to 

 produce Heat and burn; thus the Writing of Phosphorus on blue paper, 

 sufficiently rubbed, will immediately kindle into an ardent Flame, and 

 burn the Paper. (6) Those Phosphori seem to have the essential Nature 

 of Fire, because they are so easily susceptible of a burning Quality from 

 Fire; thus common Phosphorus is immediately kindled into a most ardent 

 and inextinguishable Flame by common Fire. (7) In stroking the Back 

 of a black Horse, or Cat, in the Dark, we produce innumerous Scintillae, 

 or lucid Sparks; in the same manner as rubbing a black Piece of Cloth, 

 which has hung in the Sun to dry, will cause it to throw out the Particles 

 of Light which it had imbibed from the Sun; whereas a white Piece of 

 Cloth, which reflects most of the Sun's Rays, emits no such lucid Sparks 

 in the Dark. Many other Reasons might be urged to show that Light of 

 every kind is owing to one and the same cause in a greater or lesser 

 Degree, viz. to the Velocity of the Parts of the lucid Body. 



ABBE NOLLET 



One of the colorful physicists of the mid-eighteenth century was 

 Jean Antoine, Abbe Nollet (1700-1770) , a member of most learned 

 societies, a teacher of physics to Monseigneur Le Dauphin, and Pro- 

 fesseur Royal de Physique Experimentale of the College of Navarre. 

 Abbe Nollet is perhaps best known to biologists as an early observer 



