MAG AZINE OF SCIENCE AND ART. 
163 
No. 
Name. 
Flows into. 
Latitude of 
Mouth. 
Liigtli. 
48 
28 <L 10 m- 
25 
49 
Warragamba... 
Nepean R.. 
20 
SO 
Werraminiro... 
Shoal haven R. 
15 
51 
Wingecaribbee 
IVoIlondillv R. 
25 
52 
Wolfondijlv... 
Warrairamba R- 
35 
53 
Wollomba.Thes. C. Hawk 
32 d. 12 m. 
54 
William .(Hunter R. 
do 
FREDERICK S- FEPPERCOBNE, 
Civil Engineer and Surveyor. 
Richmond River, Pec. 1st, 1857. 
PHILOSOPHICAL SOCIETY OF 
NEW SOUTH WALES. 
At the monthly meeting, held Wednesday, 
December 9th, the following interesting 
paper was read by Mr. W. S. Jevons, 
whose contributions to the Meteorology of 
this country have been so numerous and 
so highly esteemed. The paper we here 
publish will add largely to his reputation, 
and'will, we are sure, excite the earnest 
attention of Meteorologists in England. 
ON CLOUDS; 
THEIR VARIOUS FORMS, AND PRODUCING CAUSES. 
With Experimental Illustrations , ip'. 
1. Clouds, though resulting from very complex 
changes, are uniformly composed of minute parti, 
cles of water suspended in the air. The only vari¬ 
ations,.therefore, which they present are in their 
quantity or mass, and in the peculiar forms into 
which their mass is shaped. Direct observations 
on the conditions of the atmosphere in and about 
a cloud, or actual experiment upon the mode of its 
formation are, except in rare cases, quite out of the 
question ; a little reflection will show, I think, 
that the external form of a cloud, together with a 
few other phenomena, such as rain or lightning 
proceeding from it, or any peculiar motions which 
it may exhibit, are almost the only available facts 
upon which to raise an inductive theory of its 
formation. 
2. Now, the means by which I take the first 
step to explain the form of a cloud, is to produce 
experimentally, with liquids, a miniature represen¬ 
tation of it, under conditions in which the imme¬ 
diate causes can he certainly known. If it is 
found that given portions of liquids of ascertained 
specific gravities, when placed together, or vari¬ 
ously set in motion upon each oilier, produce 
peculiar appearances which exactly resemble in 
form some of the more distinct kinds of clouds, I 
assume with complete confidence that similar mo¬ 
tions and differences of specific gravity have 
operated in the production of those atmospheric 
clouds. 
It must he distinctly understood that in this first 
step we are dealing only with dynamical causes, 
that is, with simple force and motion. Liquids are. 
in many respects, very unlike gases, the latter be¬ 
ing chiefly distinguished by the property of elasti¬ 
city; but in the atmosphere this property cannot 
be directly productive of motion or force, or even 
the modification of motiou or force, because the 
air being only confined by the superincumbent air 
is always at perfect freedom to assume the density 
and elastic force due to the pressure of that air. 
Elasticity is, as it were; always self-adjusting, and 
never called into play, so that free air will resemble 
in its motions a very rare liquid, and any part of 
the atmosphere will be subject, I feel confident, to 
the same hydrodynamical laws as the interior of a 
body of liquid. 
3. But it is quite another thing to show whence 
the forces which modify the fonns of clouds are 
derived. In our miniature experiments such con¬ 
ditions are known beforehand, because we have 
prepared our liquids of different specific gravities, 
by dissolving various weighed quantities of some 
heavy soluble substance in water, and we can pro-" 
jeet the solutions thus prepared into each other, 
with any desirable velocity or direction, by the aid 
of a simple apparatus, to he presently described* 
But to explain, according to the known but com¬ 
plex properties of the atmosphere, the origin of 
those differences of specific gravity, and of those 
motions which we have established to exist in the 
formation of a cloud, is a distinct and more diffi¬ 
cult part of the subject. 
i. In the atmosphere we deal with what we may 
term the three Meteorological Elements, (the term 
element, of course, not being used in its restricted 
or chemical sense) viz.— 
1. Air. 2. "Water. 3. Heat. 
Every complicated change which heat, itself only 
a mode or disguised form of force, may occasion in 
air or water, and every disturbing effect which air 
and water, the latter in no less than three distinct 
forms, the solid, liquid, and gaseous, may mutually 
have upon each other, will have to he taken into 
consideration before wo can lay down the vera 
causa of an atmospheric cloud, as completely as ive 
can announce the conditions of our miniature, one. 
I will, first of all, describe the construction of 
my apparatus, and the mode in which the liquid 
experiments are conducted ; after which we must, 
I am afraid, go over the principal properties of air 
and water in relation to heat. AV’e shall then be lu • 
a position to discuss in particular several of the 
more distinct forms of clouds, attaining finally to 
that sublime phenomenon, a thundercloud. 
The Section-Glass. 
5. The instrument which I employ may he con¬ 
veniently termed a Section-glass, because it contains 
a thin section of liquid, which is supposed to repre¬ 
sent a section of the atmosphere. It consists of 
two sheets of plate-glass (about IS inches by 11), 
which, being let into two plain wooden frames, can 
ha so screwed together, face to face, as to form a 
water-tight vessel, containing an internal space of 
the uniform width of about § inch. This being 
tilled with water, we have a thin layer or section of 
liquid, of which the minutest motions or changes 
can be conveniently detected and observed, either 
by means of the small particles of sediment floating 
in it, or by the production of a precipitate of chlo¬ 
ride of silver, of which the component parts, silver 
and chlorine, are contained in distinct portions of 
the liquid. In the latter case, a pure white film, 
or streak of cloud, will appear wherever .the two 
solutions undergo mixture, or merely come into 
contact; and the almost infinite variety of grace¬ 
fully curved lines, and of curious and complicated 
forms thus produced, give, I think, a lively interest 
