Chap. I.] DoBritie of Bcerhaave. 89 



the degrees of heat Spirit of wine was employed by j 

 the Florentine academicians, and oil was afterwards 

 made ufe of by Sir Ifaac Newton, who conftituted the 

 points at which water freezes, and that at which the 

 lame fluid boils or aflumes the form of vapour, as 

 extreme points of his fcale of heat. Thcfe thermome- 

 ters were however fuperfeded, at leaft in England and 

 Germany, by the invention of Olaus Roemer, after- 

 wards improved by Fahrenheit, who fubftituted mer- 

 cury in the place of the other fluids which had previ- 

 oufly been employed in the conftruction of thermo- 

 meters. 



The fagacious and learned Boerhaave, both by his 

 own experiments and by his attention to thofe of others, 

 contributed greatly to the elucidation of the doctrine 

 of heat and fire. He was a ftrenuous afierter of the 

 exigence of fire as a diftinct elementary fubftance. 

 'Expanfion or rarefaction he confiders as the uniform 

 fign or criterion of its exiftence in other bodies. The 

 production of fire from the attrition of two hard bo- 

 dies, as a flint and fteel, or two pieces of hard wood, 

 &c. he accounts for, by fuppofmg that the parts of 

 thefe bodies will every moment be violently compref- 

 fed, which will excite in them, by their re-action, a 

 vibratory motion, and this will neceflfarily excite and 

 expel the fire which exifted latent in their pores ; and 

 as fire is capable of being produced in this manner by 

 the violent attrition or motion of all bodies, he infers 

 that it is prelent through every part of nature ; yet, 

 iwice it is expelled by the attrition or vibration of the 

 particles, he thinks it is clear that it does not penetrate 

 the integrant or elementary particles of bodies, bun 

 . exifts only in their pores or interftices. As fire is fup- 

 pofed to exift in all bodies, he proves its exiftence in 

 air and water; and agrees in opinion with the younger 

 JLemery, that ice is the natural ftate of water, and that 



it 



