1830.] 
319 
On the Climate of the N. W. Mountains. 
was mined, aely measured by the gauge. The stop-cock of the outer tube or case 
hV L rfn "I - an(1 W X cornincncecl i 0,ir observations. When the experiment was to 
be performed in air, the contents of the balloon were fu st rarefied, in order to ren! 
der the junctions more perfect, and the quantity of air which had been abstracted 
thpY ll” re " adm ‘ tted * Finally, when the experiment was to be performed in a gas, 
the balloon was first exhausted, a certain quantity of the gas admitted, and the 
! 7 nJR i de U s . eco ? d tu , ne 1 the full proportion of gas was then admitted, which 
7 ,nd contamina ted With the smallest possible quantity of air. 
We shall terminate this description with observing, that the dimensions of the 
leimometer had been adjusted, so that the observation of its rate of cooling might 
commence at 300 (57 2° F.) in a vacuum. The experiments in air and other gases 
demanding a little more ipanagement, and requiring the fluid to possess an eqtiili. 
ten) P era ^ ure throughout, could not be commenced much above 250° 
\4o2 r.J 
Ev^ry thing being arranged, as we have described, whether for observations in a 
vacuum, or in a gaseous medium, there only remained to observe, by means of a 
watch with seconds-hand, the indications of the thermometer at equal intervals of 
time ; these indications, however, requiring two corrections, which we shall explain, 
rust, it will be observed, that in the arrangement of our apparatus, the stem of the 
thermometer became always, in a few moments, of the temperature of the air ; each 
indication of the instrument was then too small, by a number of degrees equal to 
the quantity by which the mercury in the stem would have expanded, had it been 
raised from the temperature of the air to that of the bulb. This correction there 
was of course no difficulty in calculating, and we were careful to apply it to each 
observation. The second correction had for its object, to reduce the indications of 
the mercurial thermometer to that of air; and for this purpose, we made use of the 
table given in the first part of this memoir. 
When we had, in this way, obtained the correct series of temperatures, we applied 
the formula of calculation, which we have above explained. The series was then 
divided into several different parts, each of which was represented by expressions 
of the form m a # L - f- P ta , in which * designates the time. These served after- 
wards to calculate the rate of cooling for different excesses of temperature, which 
rates, however, required a little diminution easily determinable in eacli case. To 
understand in what tin's correction consists, it may be sufficient to remark, that the 
cooling of the bulb of the thermometer, proceeding from the loss of heat through- 
out its surface, is always a little augmented by the descent of the cold mercury from 
the stem of the instrument. Now the volume of this mercury being known, and 
also its temperature, this last correction was easily calculated, which, though very 
small, was not to be neglected. 
Such were the methods of observation and calculation followed throughout in all 
our experiments. We contented ourselves with determining the rates of cooling 
for each 20 degrees, and fearing to swell this paper unnecessarily, we have omitted 
all the intermediate steps of calculation by which the results have been established. 
We shall now proceed to the detail of our experiments, in the order in which they 
have been made. 
Our preliminary researches having taught us the influence exerted on the law 
of cooling, by the nature of the surface, it became necessary to study this law for 
different kinds of surfaces ; and it was further necessary that these surfaces should 
be such, as not to be affected by the heat to which they should be exposed. Those 
which alone appeared to fulfil this condition, are glass and silver. We have, there- 
fore, made all our experiments on a thermometer, first, with its natural surface, 
and secondly, having the bulb covered, with very thin silver leaf. These two sur- 
faces, it is known, have very different fftdiating powers ; glass being the most power- 
fully radiating of all bodies, and silver the least so. The laws to which we have been 
led, in comparing the rates of cooling, as due to these two surfaces, are so simple, 
as to be beyond all doubt general, in their application to all bodies. 
V . — On the Climate of the North- Western Mountains. 
1. A general Statement of the Weather at Subathoo, for ilfny, 1829. 
Clear, 16 # days. 
Pair, but cloudy, and partially cloudy, 9 ditto. 
