176 BIOGRAPHIES OF SCIENTIFIC MEN 



followed by " Le Perfectionnement des Therm ometres 

 et Barometres," " L' Action Capillaire," " La Fusion des 

 Vapeurs," etc. 



In 1804 Gay-Lussac, in conjunction with Alexander 

 von Humboldt, published an important memoir on the 

 chemical and physical properties of air taken at an altitude 

 of 23,000 feet. Ballooning in the early part of the nine- 

 teenth century was attended with the greatest risks ; but 

 he and Humboldt were intrepid naturalists, and under- 

 took the investigation of the atmosphere at great heights 

 hygrometry, atmospheric electricity, aqueous tension, 

 atmospheric pressure, etc., were some of the subjects in- 

 vestigated. Their memoir was published by the Academic 

 des Sciences, and contained the announcement that hydrogen 

 and oxygen combine to form water in the proportion of 

 two hundred volumes of hydrogen to one hundred volumes 

 of oxygen. It was from this discovery that Gay-Lussac 

 was led to the most important law of volumes, which 

 he discovered in 1809. This was his chef d'ceuvre ; but 

 more anon. 



Gay-Lassac investigated the nature of volcanic gases 

 more particularly hydrochloric acid gas and "the 

 vapours that rise from the fumarolles cause the sublima- 

 tion of the chlorides of iron, copper, lead, and ammonium ; 

 iron glance and chloride of sodium (the latter often in large 

 quantities) fill the cavities of recent lava streams and the 

 fissures of the margin of the crater." In the Annales de 



