Sect. V.] Meteorology. 243 



tical, and approaching to the form of a system, 

 than ever before. 



The eighteenth century is distinguished by the 

 numerous and enhghtened experiments which were 

 made during this period to ascertain the ii)cight of 

 the atmosphere in different latitudes and situations. 

 For these we are principally indebted to M. Bou- 

 guer, M. Cassan, and M. Cotte, of France; and to 

 sir George Shuckburgh, lord Mulgrave, and Mr. 

 Kirwan, of Great Bi-itain and Ireland. 



Though the experiments on the eudiometer 

 were mentioned undei' the head of Chemistry, and 

 in some respects belong to that department of 

 science, yet they also belong to Meteorology, and 

 have contributed to throw some light on this ob- 

 scure subject. These experiments, and the in- 

 quiries connected with them, belong exclusively to 

 the eighteenth century. 



At the commencement of the eighteenth cen- 

 tury, the ascent of water in the atmosphere, in the 

 form of vapour, had been but little investigated, 

 and was very imperfectly understood. Nieuentyt 

 and others had taught that the particles of lire, by 

 adhering to those of water, made up vwleciiLe, or 

 small bodies specifically lighter than air. Dr. Hal- 

 ley supposed that by the action of heat the parti- 

 cles of water are formed into hollow spherules, filled 

 with a finer air, highly rarefied, of less specific gra- 

 vity than the atmosphere, and, of course, disposed 

 to rise in it. While Dr. Desagnliers thought that 

 the ascent of aqueous particles was owing to their 

 being converted into an elastic steam. 



Such was the state of opinions with regard 

 to this fact, when Dr. Mauniton undertook the 



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