i84 GREAT MEN OF SCIENCE 



We have also to thank Dalton for the discovery that gases 

 become heated when compressed, and cooled when expanded 

 (against external pressure). The heating efTect on compres- 

 sion had been observed not long previously in air-guns, and 

 it then soon led to the invention of the pneumatic 'fire 

 syringe': Dalton showed by thorough experiments that the 

 cause of the production of heat is not friction, but a very re- 

 markable and unexpected property of all gases. ^ This later 

 became of the greatest importance, particularly to the work of 

 Carnot and Robert Mayer. 



Dalton's services to science were soon recognised by many 

 honours, which however had no influence on his circum- 

 stances in life. *He was one of those genuine, and now so 

 rare, philosophical spirits, who find so magnificent a reward 

 in the discovery of truth, that they have but little interest in 

 the passing signs of human recognition, as compared with it. '^ 

 In the year 1833, he received a small pension from the king; 

 he died eleven years later, at the age of seventy-eight. 



LOUIS JOSEPH GAY-LUSSAC {1778-1850) 

 ALEXANDER VON HUMBOLDT {1769-1839) 



These two belonged together as men of science, not only 

 because they carried out important work together and pub- 

 lished it jointly, but also on account of the continuous friend- 

 ship which united them in life, however great otherwise the 

 difference between them may have been as regards the in- 

 dividual importance of each. 



Gay-Lussac was born in a small town in the southern 

 part of France, where his father was a judge, and studied 

 technical science in Paris. He then filled various teaching 



^ See E. Mach, Wdrmelehre. 



2 Hermann Kopp, History of Chemistry, vol. i, page 364. 



