164 
MAGAZINE OF SCIENCE AND ART. 
to these experiments, while leading us, as I hope 
to’show, to the understanding of analogous move¬ 
ments on a much grander and more important 
scale. 
6. One or more glass tubes may he introduced 
in any desirable positions into the section-glass, 
through grooves cut in the opposite faces ot the 
wooden frame; and numerous currents oi liquid, 
varying as required iu velocity, volume, or quantity, 
direction, temperature, density, &c., may thus he 
introduced, so that their complex motions and re¬ 
actions may he observed in the most convenient 
manner. It is found very easy to render the whole 
watertight, if a thin continued hand of common 
glaziers putty he laid round between the level sur¬ 
faces of the wooden frames before they are screwed 
together—the tubes required for the experiment in 
preparation being likewise embedded in the same. 
One of the glass plates has been engraved by 
means of hydroiluoric acid, with two series of rect¬ 
angular lines at the uniform distance of one inch; 
these afford in every part a fixed line of reference 
to detect the slightest motions of the enclosed 
liquid, as well as to measure the rate or extent of 
that motion, if required. 
The accessory apparatus, such as tubes, funnels, 
stop-cocks, &e.", will be at once understood from 
Fig. I., in which the instrument is arranged as it 
is chiefly employed. 
7. The liquids used consist of the following 
dilute solutions, viz.:— 
1st. Water containing one part in 5000 of 
common salt or chloride of sodium (Na. C 2). 
2nd. Water containing one part in 5000 of 
crystallized nitrate of silver (Ag. O. No. 5). 
3rd. An aqueous solution, containing one- 
tenth of its weight of ordinary white sugar. 
The first two are of about the same specific gra¬ 
vity, hut produce, when they mix, a white precipi¬ 
tate of chloride of silver (chemical symbol Ag C 1), 
which, though perfectly distinct, is so thin and im¬ 
palpable as to remain a long time suspended in the 
water, the motions of which its weight does not 
perceptibly influence. Known quantities of the 
third solution are, however, added to either of the 
two former, with the object of producing such dif¬ 
ferences of specific gravity as form the required 
conditions of the experiment. 
8. A little reflection will shew that the whole 
variety of phenomena which may be produced by 
the experimental arrangements described above, 
result from only two essential variable conditions. 
1st. Originally Impressed momentum or ve¬ 
locity. 
2nd. Gravity, which is called into play when¬ 
ever we use two liquids differing, however 
slightly, in specific gravity, but which does not 
in the least affect the internal motions of a per¬ 
fectly homogeneous fluid. 
It is true we employ certain chemical salts, and 
we shall also work with liquids of different temper¬ 
atures ; but it must be borne in mind throughout 
that these are mere devices for rendering the motions 
of the liquids visible, or the latter for altering their 
specific gravities temporarily. What I wish to im¬ 
press is, that all experiments which I shall describe 
demonstrate the result of the simplest dynamical 
causes alone. With this object, the action of all 
other chemical or physical forces is, as far as pos¬ 
sible, excluded, and it is necessary that they should 
not draw off or confuse the attention. 
Properties op the Atmosphere. 
9. Having now described the apparatus, by the 
use of which we may discover what conditions of 
force and motion produce a given appearance in a 
liquid, a second step still remains to be considered 
with respect to the clouds, namely, how to translate 
these conditions, so to speak, into the language of 
the atmosphere. In other words, we must seek 
data for the minor premise of every syllogism, by 
which we would prove the real nature of a cloud. 
Given motions will produce a given form of cloud. 
What are the meteorological conditions of the at. 
mosphere which will occasion such motion, and, 
therefore, lead to the appearance of such a cloud! 
The data upon which we must do this can only 
be those for the most part long established and 
widely known, but so complex are the causes and 
effects which operate in the atmosphere, that even 
if all members of the society were acquainted with, 
the subject, it would still be an advantage to go 
over the chief points succinctly before entering 
upon a discussion in which they are involved. 
10. It is by the reactions of the three meteoro¬ 
logical elements, Air. Water, and Heat, that not 
only all the phenomena of clouds, hut also the 
whole body of facts of which the science of Meteo¬ 
rology is composed, are occasioned. We may con¬ 
sider them as follows:— 
1st. The action of heat upon Air. 
2nd. The action of heat upon Water. 
3rd. The mutual interferences of Air and 
Water. 
11. The chief property of air, a permanent gas, 
is its elasticity, by virtue of which it continually 
tends to spread itself out in every direction. The 
measure of this elasticity, or the elastic force, is di¬ 
rectly pyoportionalto the degreein which the tendency 
is restricted, or to the smallness of the space within 
which the air is confined, or, as it may' also be ex¬ 
pressed, the elastic force is proportional to the 
specific gravity or density, because the weight of a 
given portion of air always remains the same, what¬ 
ever space it may occupy. 
Thus in a vast body of air, like the atmosphere, 
the weight of the upper parts compresses the lower 
parts, and increases their clastic force and density. 
In ascending into the atmosphere, therefore, the air 
will always he found to become less and less dense, 
and the barometer, which measures the elastic force, 
will fall at some regular rate. The simple rule is, 
that at each point the elastic force is proportional 
to the weight of that part of the atmosphere which 
( lies above the point, and it would, therefore, be 
very easy to calculate the exact density and elastic 
force of the atmosphere at every elevation, but for 
the complex interference of the element heat, 
which we must now consider. 
12. The only action of heat upon air, is to cause 
it to expand in a well-ascertained ratio; 491 cubic 
inches of air, at 32 degrees, become 492 inches at 
33 degrees, 493 at 34 degrees, and so on ; that is to 
say, air, as well as all other gaseous bodies, expand 
for each degree of Fahrenheit’s thermometer 
1 -491st part of the volume they would have at the 
freezing point. But this expansion only takes 
place, of course, if they are allowed additional 
space to expand into, so that their elastic force 
shall remain the same. Supposing one cubic foot 
of air to be enclosed in an air-tight vessel, and to 
be heated ; as the weight of the air, and the size of 
the space remain unchanged, the density of the air 
within cannot vary, but in tending to expand fur- 
