Mr. W.S. Jevons on the Cirrous form of Cloud. 25 
air, with 2 (,2,) of a gramme of crystallized nitrate of silver dis- 
solved init. ‘The more gradually this stratum is inserted beneath 
the other, especially at the first, the more distinct will be the 
result of the experiment. The nicest management, indeed, and 
the most careful and patient manipulation are necessary in order 
to prevent any accidental and irregular mixture from taking 
place, which would confuse the shape of the cloud ; but even in 
his case sufficient cirrous action will subsequently go on, to 
answer the purposes of our experiment. 
A white precipitate of chloride of silver, of the usual cloud- 
like appearance, will immediately begin to form, and from the 
first will present an entirely cirrous character. Small streams 
in the form of threads or curiously shaped bands will be seen 
passing from one stratum into another, and often curving about 
in the most complicated and beautiful manner. After a time 
the middle of the glass will be filled by a dense and confused 
but still fibrous mass of cloud, which will probably soon extend 
itself to the bottom; but there will now also be seen with the 
greatest distinctness, numbers of these small parallel threads 
ascending and reaching nearly to the surface of the top stratum, 
of considerable length, and ending in evanescent points. 
The slightest circular motion or disturbance communicated to 
the strata will cause these fibres to assume all sorts of curved 
and flexuous forms, which, however, in general still maintain 
their parallelism. And it is upon the exact resemblance which 
this miniature cloud bears to the common appearances of the 
cirrus, that the probability of the truth of this theory must be 
allowed principally to rest. 
It is evident that the cloud of chloride of silver is produced 
by the gradual mixing of the upmost and lowest strata contain- 
ing respectively hydrochloric acid and nitrate of silver, thus 
representing closely the precipitation of watery particles by the 
mixture of portions of moist air of different temperatures. It 
remains then only to consider the manner and cause of mixture. 
The addition of one-eight per cent. of sugar solution was found 
to raise the specific gravity of water by about 4-10,000dths (that 
is, from 1:0000 to 1-0004 at 60° F.) ; but when heated to about 
100°, its density is not more than about ‘994 or “995, so that at 
this temperature it will lie in a separate stratum above pure water 
at 60°. 
The parts of these strata, however, which are immediately in 
contact, soon communicate their heat and tend to assume a mean 
temperature ; and it is evident that whenever this is the case, the 
portions of liquid containing sugar must always be slightiy denser 
than those that are pure, and must consequently sink below and 
displace the latter. 
