176 
MAGAZINE OF SCIENCE AND ART. 
degree the cause of your hand beiDg brought near the cat’s 
back, and rubbed upon it. The sparks are a secondary 
effect of the force expended in rubbing, and although {hey 
undoubtedly contain a minute amount of force, under a 
very peculiar form, they can have no appreciable reaction. 
Similarly the atmospheric sparks of electricity aTe a 
secondary effect of the friction of currents of air or of 
some other meteorological action, but the mechanical force 
manifested in the whole discharges of a large thunderstorm, 
amounts to a very small quantity, and is, indeed, infinitely 
small, compared with the force required to raise 
thousands of tons of water to the elevation of the clouds, 
and to stir up the winds until their pressure exerts perhaps 
a pressure of 10 lbs. on each square foot of opposing 
surface. 
SUMMARY. 
83. I will conclude this lengthy paper by stating in as 
brief terms as possible, the new results which it contains, 
chiefly suggested by the experiments described, and sup¬ 
ported by the preceding arguments: — 
1. The stratum is produced by the mixture of two 
currents of moist air, differing in temperature, but 
resting in statile equilibrium ; that is, the lower having 
the greater specific gravity. This is only a more precise 
statement of an explanation previously well known. 
2. The cirrus is produced by the ijiterfiJtration of 
two corresponding bodies of air, reversed in positiop, 
so that the lower possesses a less specific gravity than 
the upper, and cannot therefore remain in equilibrium 
3. In the acknowledged mode of the production of 
the cumulus by an ascending current of warm moi*t air, 
it has been usual to overlook some cause which operates 
to check the upward rnotluu immediately after precipita¬ 
tion has commenced. This cause may perhaps be the 
weight of the precipitated watery particles 
4. When partial subsidence or separation of the 
watery cloud particles takes place, the ascending body 
of air is not s-i much checked, and, not having the same 
tendency to re descend as in the cumulus, spreads out 
in stratiform projections, which distinguish it as the 
cumulo-stmtm. 
5. If subsidence or aggregation of the watery cloud- 
particles into rain continue and increase, the upper 
portions of the cloud, gradually relieved from rhe 
weight of the water, but retaining the heat evolved in its 
condensation, may become of less specific gravity than 
the superincumbent strata of air Upward cirrose filtra 
tion ensues, and the cumulus or oumulo-stratus is 
modified into the minims , rainxdoud or thunder-cloud, 
6. The electricity of a thunder-cloud is continuously 
derived from the weak charge originally diffused through 
the asccndiug current, which produces the cumulus and 
supplies its moisture. The precipitated watery particles 
collect this electricity, which, as they gradually aggre¬ 
gate into drops of rain, becomes intensified to an 
indefinite extent. 
89. The general conclusions to be drawn from the 
above are:— 
1. That the forms assumed by clouds, that is, by 
suspended collections of minute precipitated watery 
particles are solely determined by simple dynamical 
causes, or, in other words, by the motions occasioned by 
gravity among bodies of air differing »n specific gravity. 
2. That is unnecessary to suppose that electricity 
possesses any active agency in the production or modi¬ 
fication of clouds—a conclusion which is, on general 
grounds, highly probable. 
W. S. JEVONS, 
Double Bay, near Sydney, NSW. ( 
December 4th, 1S57- J 
REFERENCES TO THE FIGURES. 
L. Liquid of less or least specific gravity compared with 
the other portions Of liquid with which it is in 
contact. 
G. Liquid (similarly) of greater or greatest specific 
gravity. 
I. Liquid intermediate in specific gravity to two other 
portions. 
Ivor. Liquid of which the specific gravity is increasing. 
Decs. Liquid of which the specific gravity is decreasing. 
Via. IV. 
A. Ascending current of warm moist air. 
B. Plane of precipitation of cloud. f 
C. ( umulose cloud. 
D. Streams of atr descending from cloud, and spreading 
out beneath plane of precipitation. 
Figures V and VIII are drawn from photographs of the 
actual experiment. 
TRANSACTIONS OF THE AUSTRALIAN 
HORTICULTURAL and AGRICULTURAL 
SOCIETAL 
' TWEI.rTH MONTHLY MEETING. 
Held, in the Hall of the Chamber of Com¬ 
merce, Sydney Exchange. 
Tuesday, January 5tli, 1S58. 
Mr. William McDonnell in the chair. 
Members of Council present.—Messrs. 
W. McDonell, F. Creswick, JVI. Guilfoyle, 
P. L. C. Shepherd, G. A. Bell, R. 
M'fimes, T. Day, junr., W. S. Wall, T. IV. 
Shepherd, W. Deane, Hon. Secretary, Dr. 
Houston, and a good attendance of mem¬ 
bers and their friends. 
MINUTES. 
Minutes of last meeting read and con¬ 
firmed. 
PAPERS READ. 
Agricultural Associations and Improve¬ 
ment Societies, by Robert Meston, Esq., 
New England. Read by the Hon. Sec. 
On the Improvement of Pastoral Lands, 
by Henry Badgery, Esq., Bernina. Read 
by the Hon. See. 
The Secretary read the .following letter 
f.om the Rev. W. B. Clarke:— 
Sir,_In reply to your note of the oth instant, request- 
ing a geological opinion of some specimens of day accom¬ 
panying that note, from want of further data, I can only 
observe that by its appearance it is an argillaceous shale, 
bearing vegetable impressions belonging to the upper part 
of the carboniferous formation. It is, therefore, scarcely 
a clay. In reference to Mt. Scott’s inot Ascott’si note 
enclosed. I may remark that the burnt shale is nearly as 
absorbent as the unbumt, and that no conclusion could be 
drawn as to the capabilities of the material for fire brick, 
or similar purposes, from its having been subjected so 
short a time to heat, and moreover in a common fire. 
Notwithstanding it is cracked, what might be its condition 
after burning for three days in a proper furnace, J cannot 
say 
Fire clay is a partially artificial substance, and contains 
some mineral constituents probably not found in these 
specimens. 
f would suggest to you that if there be any object in 
view, it,would te well to submit the substance to a 
chemist who?e province it is to test its character as to in¬ 
fusibility and quantitive as well as qualitive constituents. 
I have the honor to be. Sir, 
• Your obedt. Servant, 
W. B. CLARKE. 
A vote of thanks was proposed by Mr. 
Thomas Day, junr., seconded by Mr. P. 
L. C. Shepherd, and carried by acclama¬ 
tion, to Robert Meston, Esq., for bis parer 
