396 Intelligence and Miscellaneous Artictcs. 



for the number of English pounds which the heat necessary to raise 

 one English pound of water from 32° to 212° is capable of raising 

 one inch. 



Joule found by experiments on the heat produced by friction 10680. 

 By experiments on the heat evolved by the compression of air he 

 found 9876 and 9540. All these numbers agree tolerably well. — 

 Poggendorff's Annalen, 1852, No. 6. 



ON THE RAIN-WATER COLLECTED AT THE OBSERVATORY AT 

 PARIS. BY M. BARRAL. 



Up to the end of the seventeenth and beginning of the eighteenth 

 centuries the atmosphere was reckoned amongst the few elements 

 admitted at that time. In course of time the researches of Van Hel- 

 mont, Hales, Mayow, Bergmann, Scheele and Lavoisier, led to the 

 knowledge of the fact that the atmosphere is a mixture of oxygen 

 and nitrogen. The later chemists set themselves to the task of de- 

 termining these constituents with greater exactitude than was pos- 

 sible to their predecessors. Thus Cavendish, Davy, Marty and 

 BerthoUet showed that the air had the same composition in all cli- 

 mates. Gay-Lussac ascertained the same fact with regard to air 

 obtained by him by means of an air-balloon from a height to which 

 no one had previously attained. He, together with Humboldt, 

 furnished considerable assistance to Lavoisier in his determinations. 

 Afterwards, in 1822, Despretz made numerous analyses of the air 

 and arrived at similar results. Lastly, Dumas, Boussingault and 

 Regnault have carried the accuracy of the analyses much further by 

 operating upon larger quantities of air ; and it appears that posterity 

 has nothing more to determine, except whether the ascertained com- 

 position of the atmosphere be constant, whether the causes, such as 

 combustion, respiration, &c. which lessen its quantity of oxygen, are 

 accurately compensated by the known sources of oxygen. The atmo- 

 sphere contains also vapour of water and carbonic acid. It is not yet 

 ascertained Avho first discoA'ered the presence of the latter ; Black 

 proved, immediately after the discovery of carbonic acid, that the thin 

 crust which is formed upon lime-water when exposed to the air, 

 consists of carbonate of lime. 



All the preceding statements referred to the atmosphere in a state 

 of purity. But winds, storms, and the ascending current of air pro- 

 duced by inequality of temperature, bear dust and particles of water 

 from the foam of the sea, with the air which has been in contact with 

 the ground, into higher regions. Such is, for instance, the red rain, 

 with which the philosophers of the seventeenth century, Wcndelin, 

 Descartes, Peiresc and Gassendi, occupied themselves to such an 

 extent. 



It was only towards the middle of the last century that it was felt 

 that the causes of such variations must be ascertained by regularly 

 continued observations. These were undertaken at first only with 

 the view of determining how far from the point of their origin such 

 perturbations extend themselves. The study of rain, which, as it 



