194 Proceedings of the Royal Physical Society, 



contrary, produced by the action of fire. He supposes the 

 globe to have experienced sucli a degree of heat as to have 

 been reduced to a state of igneous fusion or liquefaction, and 

 that, as the mass cooled, each mineral substance became 

 crystallised, either regularly or in a more confused manner, 

 according to the laws of affinities. 



The names of three other famous writers and discoverers of 

 this period occur to me as right to be mentioned. I mean 

 La Place, the voluminous writer on the Cosmos ; Lavoisier, 

 the chemist ; and Sir William Herschel, the astronomer. 



In 1796 La Place gave a popular account of his numerous 

 discoveries in physical astronomy in his " Exposition du 

 Systeme du Monde," written with much taste and eloquence. 

 This work " made a sensation in Europe, and widely extended 

 the reputation of its author." This prolific Avriter and pro- 

 found thinker died in 1827. 



Lavoisier was, perhaps, the greatest chemical philosopher 

 France ever produced. He succeeded in exploding the then 

 fanciful doctrine of phlogiston, and by the combustion of the 

 diamond demonstrated its true nature. This talented man 

 perished at a comparatively early age on the scaffold, a victim 

 of the reign of terror during the French Eevolution. 



Sir William Herschel, a native of Hanover, originally a 

 musician of some note, was employed in this country as such, 

 but having after a while discarded music for astronomy, he 

 first became famous in this last science by the construction of 

 admirable and powerful telescopes and specula, whereby he 

 made many remarkable discoveries in the heavens. In 1781 

 he discovered the planet Uranus, first called the Georgiuin 

 Sidus. " His researches on double, triple, and multiple stars, 

 on nebulae and clusters of stars, on the motion of the solar 

 system in space, were vast accessions to sidereal astronomy." 

 His death occurred in 1822. 



Dr Priestley, the discoverer of oxygen, and of various other 

 forms of gases, must be mentioned as an author of mark of 

 the period under review, together with Dr Black, the dis- 

 coverer of latent heat, also Henry Cavendish, who determined 

 by experiments the mean density of the earth, and who is 

 also considered by some to be the discoverer of the composi- 



