84 Biographical Account of [Feb. 



permanent hydrogen lamp, so well known in Germany, 

 which lights itself by the most ingenious application of the 

 electrophorus ; and lastly, the eudiometer, which is still an 

 indispensible instrument in the analysis of gases, and has 

 enabled us to ascertain, that notwithstanding the immense 

 consumption of oxygen by men, quadrupeds, and birds, in 

 the act of respiration, and its necessary support of combus- 

 tion, whether we examine atmospheric air in the scorch- 

 ing equitorial regions, over the immensity of the ocean, the 

 elevated plains of Asia or America, the snowy summits of 

 the Cordillera or Himmalays, the proportion of oxygen 

 remains constant. Humboldt, Gay Lussac, and others, 

 have investigated the accuracy of different eudiometers, 

 and have found that Volta's is by far the most accurate. 

 In connexion with this subject, although not in chrono- 

 logical order, may be mentioned the experiments which he 

 published in 1793, upon the dilatation of air. 



This question had attracted the attention of philosophers, 

 the results of whose experiments were very discordant. 

 Volta discovered the cause of these differences and shewed, 

 that in experimenting in a vessel containing water, we 

 ought to find increasing dilatations ; that, if there is not in 

 the apparatus any moisture but what usually covers the 

 glass, the apparent dilatation of the air may be increasing 

 in the lower part of the thermometric scale, and decreasing 

 in the upper part ; he proved by delicate experiments, that 

 atmospheric air, if it is contained in a vessel perfectly dry, 

 dilates in proportion to its temperature, that is, the elasti- 

 city of a given volume of atmospheric air is proportional to 

 its temperature. 



When we heat air taken at a lower temperature, contain- 

 ing always the same quantity of moisture, its elastic force 

 increases like that of dry air. Hence, Volta concluded that 

 the vapour of water and air, properly speaking, dilate in the 

 same way, which is now known to be correct. Our know- 

 ledge upon this subject is, by the labours of Gay Lussac 

 and Dalton, now complete. They made their experiments' 

 before those of the Italian philosopher were known either 

 in England or France. 



We come now to the researches of Volta upon the elec- 

 tricity of the atmosphere; but before considering them, it 



