168 BIOGRAPHIES OF SCIENTIFIC MEN 



copper and zinc). This battery, although non-existent 

 now, was the means of producing valuable discoveries in 

 the hands of Gay-Lussac and Thenard. 



Davy proved that oxygen was not the acidifying 

 principle of acids, as stated by Lavoisier ; and he led 

 the way to the ultimate definition of an acid. 



In 1803 Davy was elected F.R.S. ; in 1807, Secretary 

 of the Royal Society ; and in 1820, its President. During 

 these years a vast number of papers were published by 

 him ; and he published the following books : Elements of 

 Agricultural Chemistry (1813); Elements of Chemical 

 Philosophy ; Salmonia, or Days of Fly-fishing ; and 

 Consolation in Travels, or the Last Days of a Philo- 

 sopher (published in 1831, two years after his death). 

 The last-named book contains some finely written theories 

 on ethical and moral questions, with descriptions of 

 Italian scenery. 



In his book on Agricultural Chemistry, Davy 

 says : 



Agricultural chemistry has not yet received a regular and systematic 

 form. It has been pursued by competent experimenters for a short 

 time only. ... I am sure you will receive with indulgence the first 

 attempt made in this country to illustrate it by a series of experimental 

 demonstrations. ... It is evident that the study of agricultural 

 chemistry ought to be commenced by some general inquiries into the 

 composition and nature of material bodies, and the law of their changes. 

 The surface of the earth, the atmosphere, and the water deposited from 

 it, must either together, or separately, afford all the principles concerned 

 in vegetation ; and it is only by examining the chemical nature of these 

 principles that we are capable of discovering what is the food of plants, 



