August 27, 1885 | 
NATURE 
407 
means of distinguishing between them—namely, by the character 
of the solar and lunar halos which are very often seen in thin 
veils of clouds. It has been established beyond doubt that the 
rings of light of larger size, or halos of about 22° diameter, are 
caused by refraction in ice crystals. (This angle is that of the 
least deviation for rays of mean refrangibility in passing through ice- 
prisms of 69°). On the other hand the smaller rings (coronz) of 
from 1° to 6° diameter owe their origin to the refraction of light 
through spheres of uniform size. Halos are not nearly so rare 
as is commonly supposed. M. Galle observed seventy-eight 
halos and about as many parhelia in a year and a half, and 
often even in the heat of summer. Kamtz laid great stress on the 
importance and infallibility of this optical means of distinguish- 
ing between the two classes of clouds. 
After these preliminary considerations let us turn to thunder- 
storms. The local or heat thunderstorms (identical with most 
summer thunderstorms) are best known, while the large cyclonic 
thunderstorms have been less investigated. In the first case, 
the appearance of the clouds which rise high in the sky as 
gigantic columns of cumulus, show that they owe their origin to 
a strong ascending current of great humidity. According to 
Dr. Reye, the principal condition for the formation of a con- 
tinuous ascending moist air current is the abnormally rapid 
decrease of temperature in its vicinity, while in the current itself 
the decrease of temperature with height is essentially retarded, 
owing to the latent heat set free by the condensation of vapour. 
Under these conditions, the distribution of temperature in the 
atmosphere is therefore such that the isothermal surface of zero 
in the ascending current is raised especially high, while outside 
this current the surface has an abnormally low position. In this 
way, therefore, water still in a liquid state reaches the ice- 
region ; ice-clouds and water-clouds must exist side by side. 
If the moist current rises sufficiently high its temperature sinks 
below o° C. and this gives rise to cirrus clouds of snow and hail, 
which latter frequently accompanies thunderstorms. Kamtz has 
shown from his observations in high mountains that the height 
of the locus of thunderstorms must not be placed too low ; the 
usual estimations of the height of thunderstorms based upon 
observations of lightning and thunder cannot be taken into 
account here, for they only show (and that very inaccurately) 
the position of the lowest structure of the thunderstorm 
clouds. 
Both Hann and Kamtz agree that water and ice clouds always 
exist simultaneously in the sky, and not only during local 
thunderstorms but also during those of the other kind. Hann 
describes the layers of ‘‘cirrostratus” cloud as always existing with 
thunderstorms. Kamtz has always been able to recognise halos 
i.e, the characteristic indication of the presence of ice particles 
before thunderstorms, as soon as he could trace the change from 
clear sky to thick clouds. And in all three of the previously 
mentioned balloon ascents on days of thunderstorms ice particles 
have been observed in the air. 
We may take it that it has been established that in every 
thunderstorm clouds composed of water particles and others of 
ice particles exist simultaneously side by side, and that, of 
course, they are, mutually changing places it is very easy to 
suppose that the friction of water particles and ice particles may 
serve as a source of electricity. But this is in no way a mere 
supposition, for it is a fact already established by Faraday. In 
his experiments on the cause of the production of electricity in 
Armstrong’s steam electrical machine, which was considerably 
modified by him, he frequently caused compressed air to strike 
against solid objects. The cooling arising from the expansion 
of the air caused a copious formation of fog, and the friction of 
these particles against the objects always excited the particles 
with + electricity and the solid objects with — electricity. It 
was only by the friction of the particles against ice that the 
latter became + on every occasion, while wood and metal 
were excited with — electricity by the friction of the particles. 
I have frequently repeated these experiments of Faraday’s, 
and, as was to be expected, entirely confirmed them, Of course 
several precautions must be taken if we do not wish to be 
checked by evidently contradictory results. The principal 
causes of disturbance may arise by the carrying away of particles 
of grease from the greasing of the taps, and on the other -hand 
by the friction of the particles on the walls of the tube, if the 
turning on is not quick enough. In the latter case the particles 
become + and communicate this electricity to the objects they 
meet, and thus, therefore, the character of the electricity by 
friction with these bodies is partially or wholly masked. “The 
colder the ice the more powerfully it becomes electrified—a fact 
which appears to be in connection with the increase of its insu- 
lating power with decreasing temperature.? 
Tf, therefore, air-currents flow against each other, one being of 
ice particles and the other of water prtticles, the ice particles 
become positively and the water particles negatively electrified, 
and as by no means a rapid mixing of both kinds of air-currents 
is'requisite, which may be seen z#fer alia from various observations 
on smoke-laden air-currents in laboratories, the oppositely 
electrified bodies are quickly repelled from each other. 
The real cause of thunderstorm electricity appears to me to lie 
in the sequence of phenomena above described. It is not my in- 
tention to discuss the behaviour of the further phenomena con- 
nected with thunderstorms. 
A more detailed exposition of the theory very briefly sketched 
here, as well as the observations used for its proof, will be found 
in my Treatise on the Origin of Thunderstorm Electricity and of 
the Ordinary Electricity of the Atmosphere, just published by 
G. Fischer, Jena. (‘‘Der Ursprung der Gewitter-Elektricitat, 
und der gewohnlichen Elektricitat der Atmosphare.”) 
CYSTOLITEHS: 
M J. CHAREYRE! has made a detailed examination of 
* these structures in plants belonging to the Urticacez, 
and to many other families. 
chief results :— 
In the Urticacez the prolonged action of darkness causes 
complete disappearance of the calcium carbonate in the cysto- 
lith, though without their mass sustaining any diminution ; 
they retain completely their original form. This takes place 
before the etiolation which is the result of placing the plants in 
question in the dark. It is due probably to the cessation of the 
action of chlorophyll. Calcium oxalate disappears in the same 
way from the cystoliths. The lime set free by the decomposition 
of these salts collects in the stem, where it exists in combination 
with some other acid. 
In the Acanthacez, on the other hand, none of these phe- 
nomena are exhibited, and the cystoliths undergo no change 
from the action of darkness ; and this difference in the behaviour 
of the cystoliths in these two natural orders appears to cor- 
respond to no less important differences in their constitution. 
The calcium carbonate appears in one family in the crystalline, 
in the other family in the amorphous, form. 
All the seeds of Urticaceze examined before germination pre- 
sented reservoirs of food-material consisting exclusively of 
aleurone, in each of which was a rounded globoid. The same 
was the case with the Acanthacez, except Acanthus and Hexa- 
centris coccinea, plants containing no cystoliths, and in which the 
reserye-material of the seeds consists chiefly of starch. The 
calcareous reserve-material contained in the seeds in the form of 
globoids disappears more rapidly when they germinate in a soil 
formed of pure silica than in ordinary soil, or in one composed 
of calcium carbonate. But no part of this reserve-material con- 
tributes to the formation of deposits of calcium carbonate, whether 
as cystoliths or in any other form, nor to the production of 
crystals of calcium oxalate. In seeds which germinate in pure 
silica the cystoliths do not arrive at full development; the 
pedicel is formed, but no deposition of either cellulose or lime 
takes place at its extremity. In soil composed of calcium 
carbonate the cystoliths appear at the same time as in ordinary 
soil, ze. at the moment when the green cotyledons are dis- 
engaging themselves from the seminal envelopes, but their develop- 
ment is somewhat more rapid. Seeds sown in ordinary soil or 
in calcium carbonate, but kept in darkness, give rise to rudi- 
mentary cystoliths without any calcium carbonate. 
Yellow dying leaves of many Urticacez present, as contrasted 
with green leaves, cystoliths containing a smaller quantity of 
calcium carbonate, but this is not the case with Acanthacez or 
with Pilea. 
Both the calcium carbonate in the cystoliths and calcium 
oxalate are believed by the author not to be merely products of 
excretion, but to play an important part in the life of the 
plant. 
The following are some of the 
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