326 A method of cooling the Air of [No. 10, new series. 



the air in the tube ; and the result of that is a lowering of the 

 temperature. But it will soon be warmed up again, by the con- 

 duction and radiation of the pipe, to the heat of the water, or to 

 its original temperature ; and then, on being extracted by the 

 pump, and thrown out into the atmosphere, it will be compressed 

 to its original density : and will then rise above the heat of the 

 surrounding atmosphere, to a degree proportioned to the compres- 

 sion so occasioned. The warming is thus produced at once where 

 it is wanted, and has not, as in the former case, to be communi- 

 cated slowly by conduction and radiation through the copper, from 

 air on one side to air on the other ; a very slow plan, on account 

 of the small conductive power of gases. 



Cor. 2. — In preparing and fitting the tropical air for the pur- 

 poses of human life, we have hitherto considered only its affections 

 as to heat and moisture ; but there may, doubtless, be many gases 

 and finely divided substances diffused through it, giving it many 

 of its unhealthy qualities. Chemical analysis has not yet been 

 able to detail them, but that is rather from the comparative rude- 

 ness of the methods, than from the non-existence of the extrane- 

 ous matter ; for the sense of smell may often be powerfully affect- 

 ed, as with the scent of plants, and yet a chemist is unable to dis- 

 cover anything different in the air immediately round a plant, and 

 at a little distance from it. One reason of the non-success which 

 has attended analysis of air, would seem to be the small quantities 

 of air usually operated upon ; so small, indeed, that it is jnot to be 

 expected that the foreign substances should make themselves ap- 

 preciable in the nicest balance. 



Our cooling machine, however, forms at once an apparatus in 

 which air may be analysed on as large a scale as may be desired ; 

 for it is only necessary to half fill the worm pipe in the cooling tub 

 with such chemical fluid as the aerial impurities may be expected 

 to combine with ; and the machine being put to work in the usual 

 way, will pump all the air through the fluid, and to an extent of 

 several tons weight of air in the course of the day ; so that then 

 the smallest admixture of any foreign substance would have so 

 accumulated its effect on the fluid, as to be most probably sensible 

 to ordinary chemical examination. 



