Leslie on Meteorology. 181 
is “ Law of Atmospheric Solution.” We need only say in re- 
ply to this strange doctrine, that his indicator must be griev- 
ously fallacious, since it has been determined by the concurring 
experiments of every modern chemist, who has ever treated the 
subject, that equal bulks of dry hydrogen gas, and of common 
air, confined over water, at the same temperature, become asso- 
ciated with exactly the same weight or volume of aqueous ya- 
pour; or one of the former, by weéght, acquires as much as 
14.4 of the latter. 
The following passage exhibits, we conceive, a singular per- 
version of philosophical research. We shall give it without com- 
ment. To discover the precise law, by which equal additions of heat 
augment the dryness of air, or its power to retain moisture, is a problem of 
great delicacy and importance. Two different modes were employed in 
that investigation, but which led to the same results. The one was, ina 
large close room, to bring a hygrometer conjoined with a thermometer, 
successively near to a stove intensely heated, and to note the simultaneous 
indications of both instruments, or to employ two nice thermometers, pla- 
ced beside each other, and having their bulbs covered respectively with 
dry and with wet cambric. By taking the mean of mary observations, and 
interpolating the intermediate quantities, the law of aqueous solution in air 
was laboriously traced. But the other method of investigation appeared 
better adapted for the higher temperatures. A thin hollow ball of tin, four 
inches in diameter, and having a very small neck, was neatly covered with 
linen ; and being filled with water nearly boiling, and a thermometer in- 
serted, it was hung likewise in a spacious close room, and the rate of its 
cooling carefully marked. The experiment was next repeated by suspend- 
ing it to the end ofa fine beam, and wetting with a hair pencil the surface 
of the linen, till brought in exact equipoise to some given weight in the op- 
posite scale ; ten grains being now taken out the humid ball was allowed to 
rest against the point of a tapered glass tube, and the interval of time with 
the corresponding diminution of temperature, observed, when it rose again 
to the position of equilibrium. The same operation was successively re- 
newed; but as the rapidity of evaporation declined, five, and afterwards 
two, grains only were, at each trial, withdrawn from the scale. Fromsuch 
a series of facts, it was easy to estimate the quantities of moisture which the 
same air will dissolve at different temperatures, and also the corresponding 
measures of heat expended in the process of solution *. 
As if the above were not enough to mystify what Mr. Dalton 
and M. Gay-Lussac, and others, have long ago made sufficiently 
clear, he next presents us with a small table of the solvent power 
of air, from the temperature of fifteen centigrade degrees below 
zero, to forty-four above it; or from 5° Fahr. to 112.2°! 
We have now, we believe, adduced sufficient evidence, that 
this long section on the hygrometer is equally erroneous in phi- 
losophical principle, as it is deficient in practical utility. Such 
of our readers as wish to acquire correct information on this 
matter, may consult with advantage Mr. Dalton’s various me- 
moirs already alluded to, Mr. Daniell’s papers in this Journal, 
and M. Biot’s chapter in the first part of his Trazté de Physique, 
on the relation between air and moisture. 
* Pp. 341 and 342. 
