8 BIOGKAPHIES OF SCIENTIFIC MEN 



a hundred years. A theory is only useful when it explains 

 the truths of science and helps the advancement of know- 

 ledge. Many theories have disappeared from the realms 

 of science, and many are undergoing modification even 

 at the present day. 



About eleven years (1785) after the succession of Louis 

 XVI. to the throne of his grandfather, the phlogistic 

 doctrine was completely overthrown and this was entirely 

 due to the researches, philosophical deductions, and writings 

 of the great Frenchman. 



Lavoisier gave the present accepted definition of an 

 " element," although it may be remarked en passant 

 that the researches of Lockyer, Eamsay, and others in the 

 present day have somewhat modified our views concerning 

 the nature of the chemical elements. 



About the years 1785-87 Lavoisier, aided by De 

 Morveau (a convert to the nouvelle chimie), Berthollet, and 

 De Fourcroy, formulated a new system of chemical nomen- 

 clature which was greatly needed for the further develop- 

 ment of the Lavoisierian chemistry : elements, compounds, 

 oxides (peroxides and protoxides), acids, salts, etc., were 

 defined, thus forming the basis of the chemistry of to-day. 

 Lavoisier was the general who marshalled the isolated 

 facts and co-ordinated them into one harmonious and 

 stupendous whole. The work of the four French chemists 

 and the teaching of Lavoisier were, by the close of the 

 eighteenth century, universally accepted by chemists. 



