LECTURE II. 



REVOLUTION OF THE VIEWS REGARDING COMBUSTION PRIESTLEY 

 SCHEELE LAVOISIER INDESTRUCTIBILITY OF MATTER. 



A STRUGGLE of great importance for chemistry was carried on 

 between the years 1774 and 1794. This struggle was con- 

 cerned with the removal of the fetters laid by the Greek 

 philosophers upon the thinkers of that period, and with the 

 consistent upholding of the Baconian philosophy. It had to 

 do with the recognition of the experimental method (or the 

 method of observation under definite conditions) as the basis 

 of all theoretical conclusions and speculations ; and with the 

 clearing away of those prejudices which had been created in the 

 minds of the period by the method followed for centuries, 

 that, namely, of giving the foremost place to speculation, and 

 of adapting observed facts, as well as might be, to the estab- 

 lished system. 



These twenty years are not only rendered conspicuous by 

 a series of brilliant experimental investigations, but they possess 

 also a universal importance in chemistry because they led to 

 the establishment and recognition of a principle which consti- 

 tutes the basis of all our chemical experiments ; and which is 

 to so great an extent involved in our general scientific con- 

 siderations, that deviations from it seem inconceivable to us< 

 This is the principle of the Indestructibility of Matter. It is only 

 with the greatest effort, and from an extremely objective stand- 

 point, that we are in a position to understand scientific treatises 

 in which this basis is wanting. 



Although innumerable experiments are in agreement with 

 this principle, yet we must be doubly careful in the adoption 

 of any such law, seeing that it constitutes the basis of all our 



