CHEMISTRY OF THE NINETEENTHS CENTURY. 611 



wire gauze held in a candle or gas-flame, exhibits 

 the fundamental principle of the Davy lamp. The 

 combustible gases can be ignited on one side of 

 the gauze, which does not permit the flame to pass 

 through. The original papers show that this is 

 owing to the power of the wire to rapidly abstract 

 heat from the ignited gases. The fact of claims for 

 prior or independent invention of the safety lamp 

 having been advanced in favour of Dr. Clanny and 

 in favour of George Stephenson, the eminent engi- 

 neer, does not detract from the merit of Davy's 

 scientific treatment and successful solution of the 

 problem. The safety lamp is a striking instance of 

 science bearing "fruit" in the Baconian sense. 



In a preface to a separate publication (1818) of 

 his researches relating to this subject, we find Davy 

 expressing indebtedness "to Mr. Michael Faraday 

 for much able assistance in the prosecution of my 

 experiments." Some notice of Faraday's scientific 

 career has been given in the chapter relating to elec- 

 tricity; but his discoveries in chemistry were neither FJG it _ DAVY - S 

 few nor unimportant, and some of these will be SAFETY LAMP. 

 noticed further on. 



The atomic theory of Dalton, like perhaps every other theory when 

 first propounded, met with some opposition. The French chemist 

 Berthollet, to whom the science is indebted for many valuable re- 

 searches, called in question the fact of definite proportions in com- 

 binations. Berthollet's own investigations into " chemical affinity " 

 are held to be classical. They were conducted to discover the opera- 

 tion of a special force called " chemical affinity," which was supposed 

 to govern the combinations of bodies, and they brought to light a 

 number of valuable truths. Berthollet considered that certain forces, 

 such as cohesion and elasticity, opposing the action of affinity, might 

 in certain cases more or less neutralize each other, so as to leave the 

 action of affinity unimpeded. Combination of elements might then 

 take place in any proportions, which would be determined only by the 

 masses of the substances taking part in the action. Dalton's law of 

 combination in unvariable proportions is of course inconsistent with 

 these views, and therefore Dalton's facts and theory were opposed by 

 all the weight of Berthollet's authority. Dalton's views, however, were 

 with equal vigour supported by another Frenchman, PROUST (17 . . 

 ....), who answered Berthollet's cavils by bringing forward more 

 exact analyses of oxides and sulphides in confirmation of the law. 

 The dispute lasted from 1801 to 1808, and resulted in the establish- 

 ment of the Law of Definite Proportions. 



A new proof of the validity of the laws of definite proportions was 



392 



