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Wow. 7, 1872) 
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many valuable papers were read, followed by fruitful dis- 
" cussions ; a final general meeting to listen to something 
that would interest all, and then the dispersion. This 
_ Society appears to be satisfactorily accomplishing its pro- 
_ fessed aim of increasing the interests of the people gene- 
rally in scientific studies of establishing intimate and 
familiar relations between men of science engaged upon 
‘the same subject, and of fostering a harmonious spirit of 
~ labour all over the country. We give an abstract of the 
report contained in the Bibliothégue Universelle. 
_ Prof. Volpicelli gave a paper on Atmospheric Electricity 
and the best method of studying it. Having made ex- 
periments, in calm weather, according to the methods 
both of Franklin and of Peltier (in the former of which a 
fixed uninsulated rod is used, connected with an electro- 
meter by a wire, while in the latter a moveable metallic 
_ point with similar connection is sent up into the atmo- 
sphere), he found the results always contradictory as re- 
_ gards the quantity, and sometimes also as regards the 
_ quality, of electricity indicated. ’ 
On all the days in which the air was not much agitated, 
‘the time and circumstances being the same, the moving 
_ rod gave a greater quantity of electricity than the fixed ; 
and the former often showed positive electricity, while 
the latter showed negative. 
It has been shown that the earth is a body negatively 
electrified. It follows that any conducting substance is 
electrified positively when it rises in the atmosphere, and 
becomes negative, on the other hand, asit descends. The 
indications of the metallic rod shot into the air are there- 
fore modified by the influence of the earth, and do not 
_ give a means of determining the electricity of the sur- 
‘rounding atmosphere. Franklin’s fixed rod, on the other 
hand, is free from these disturbing influences. 
__ That aconductor gives positive electricity as it rises in 
_ the atmosphere, and negative as it descends, may be 
_ proved by experiment. Suppose, e.g., the fixed rod gives 
negative electricity ; if a flame be applied to the point 
of it, the apparatus will indicate positive electricity, The 
_ flame produces an upward current of air, which, by its 
motion, and under the influence of the earth, gives a 
neutralising positive electricity, so that the point of the 
fixed rod becomes positively charged. (It is necessary 
that the flame should have a high calorific power.) 
If the flame be now brought down to the ground, one 
or other of three effects will occur :—if the flame is not 
very strong, negative electricity will be indicated ; if 
_ somewhat hotter, there will be no electricity at all ; if 
very intense, the electricity will be positive. These effects 
are readily explained as the resultants of two opposing 
actions, the production of positive electricity by the as- 
cending current of air, and the production of negative 
through the influence of the earth on the descending 
flame. The general inference Prof. Volpicelli draws is 
the preferability of Franklin’s method to the other. 
[ M. Miiller, professor at Fribourg, gave an account of 
_ experiments on the lower Glacier of the Grindelwald, with 
‘reference to the optical properties of glacial ice. His 
experiments partly confirm the results obtained by MM, 
Grad and Dupré, that thin lamellz of ice cut horizon- 
tally at the base of the glacier, give, in Norremberg’s 
_ apparatus, systems of coloured rings with a dark cross, 
This property, moreover, appears only at certain separate 
‘parts of the lamella, and the system of rings is always 
‘more or less incomplete, which is sufficiently explained 
by the irregular structure of the ice of glaciers, in which, 
“necessarily, there are only distant traces of the mode of 
_ original formation, Vertical sections gave no coloured 
rings. 
NL Louis Dufour described some important researches 
on the Diffusion of Gases across diaphragms and the vari- 
ations of temperature accompanying it. He studied the 
_ cases (among others) of hydrogen and air, of air and car- 
bonic acid. : 
o 
(TURE A 
He distinguishes the diffusion at constant pressure, and 
the diffusion with change of pressure, The porous vessel 
containing the gas with slower diffusion contains also a 
very sensitive thermometer, and is enclosed in another 
vessel, in which the other gas circulates. A glass tube, 
passing through the stopper of the porous vessel, can be 
put in communication either with external air (pressure 
constant) or with a manometer, The whole is enclosed 
in an envelope of cotton. The thermometer is observed 
with a cathetometer. 
1. Diffusion at constant pressure.—First of all, taking 
as example hydrogen and air, equilibrium of temperature 
is established between the air outside of the porous vessel 
and that inside; then hydrogen is made to circulate, and 
it is seen that the thermometer in the interior falls, A 
large number of experiments showed that there is always 
a rise of temperature on the ‘side of the entering gas, 
and a fall of temperature on the side of the escaping gas. 
M. Dufour believes this change of temperature does not 
take place throughout the gaseous mass, but only at the 
surface of the diaphragm, He conceives that at the part 
where the gas enters there is condensation and compres- 
sion, causing development of heat. In the opposite case 
vices is expansion of the gas, and hence absorption of 
eat, 
2. Diffusion with change of pressure,—In this case the 
phenomenon is complicated by variations in the tempera- 
ture according to the pressure. When the diffusing gas 
enters the porous vessel, the thermometer indicates first 
a slight rise of temperature resulting from rapid increase 
of pressure ; it then falls, and to a much greater extent 
(jj of a degree e.g.) commences again to rise gradually, 
falls a little again, in consequence of the escape of the 
other gas and the rarefaction produced ; then continually 
rises. The effects are represented by a curve. 
M. Dufour also studied the case of diffusion between 
dry air and moist air. He observed there was 
always diffusion between two quantities of air having 
different degrees of humidity; and, contrary to what 
one might expect from Graham’s law (the vapour of 
water being lighter than air), the diffusion takes place 
from the dry to the humid. The laws of variation of 
temperature in this case conform to what M. Dufour ob- 
served in the case of two gases. The diffusion is readily 
indicated by a water manometer, and M. Dufour thinks 
the principle might be applied in hygrometry. It is evident 
that the general principle must have numerous applica- 
tions in the organic world. M. Reichert described a 
thermo-regulator, in which the mercury of a thermometer 
which was placed in a heated liquid interrupted, on rising 
to a certain point, the passage of the heat-producing 
gas. 
M. Mousson described a method for measuring the 
dispersion in the different parts of the spectrum furnished 
by a prism or any spectroscope whatever. The dispersion 
varies, it is known, in the different portions of the spectrum 
obtained with a prism, it is believed much less rapidly in 
the red, much more rapidly in the violet. The law 
according to which it varies changes according to the 
different prisms and different substances used. M. 
Mousson proposes a new simple process by means of 
which the law can be directly determined for each spectro- 
scope. It consists in observing with the spectroscope 
the spectrum given by a network (réseau) of diffrac- 
tion, of which the lines ought to be perpendicular if 
the edges of the prism are horizontal. There is thus 
obtained a curved spectrum, which is the graphic repre- 
sentation of the law sought. : 
Other papers in the section were by M. de la Rive on the 
rotation of the electric discharge in rarified gases under the 
influence of a magnet, and particularlyupon the mechanical 
action which this discharge could exercise in its rotating 
movement. M. E. Hagenbach expounded the principal 
results of his beautiful researches upon Fluorescence : 
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