548 Natural History, [Ghap. III. 



)i(n'af iires being brought into contact or a state of 

 mixture; and, at a third, by supposing this event 

 to be produced by the conversion of oxygen and 

 hydrogen gases into water, according to the ex- 

 periments of Cavendish, Lavoisier, and others. 

 TJiese several opinions have been successively po- 

 pular in the course of the century, and will be 

 fouiid amply detailed in the writings of Hamilton, 

 Ilutton, dc Saussure, and de Luc, on this sub- 

 ject. But, after all, it must be acknowledged 

 that great difficulties attend every theory hitherto 

 formed with a view to solve this question: inso- 

 much that the greatest meteorologist of the age, 

 ]\L de Luc, after making a more patient, accu- 

 rate, and thorough inquiry into the subject than. 

 V, as ever accomplished by any other man, seems 

 to be at a loss to furnish a satisfactory account 

 of the matter. He therefore contents himself with 

 concluding, that the air formed by the decompo- 

 sition and ascent of water becomes reconverted 

 into that fluid by some unknown cause, or by a 

 combination of causes, and falls in the form of 

 niin, hail, or snow, according to the circumstances 

 in which the reconversion takes place, or the state 

 of the regions through which it passes in its de- 

 scent. 



Much light has been thrown, in the course of 

 the last century, on the varieties of temperature 

 in difierent seasons and latitudes. On this subject 

 Dr. Halley made some instructive observations. 

 _\ few years afterwards, M. de ISIairan, an in- 

 genious French meteorologist, by a series of ob- 

 servations and experiments, discovered that the 

 rigour of tlic winter's cold is tempered by the heat 



