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POPULAR SCIENCE REVIEW. 
cell. Its action is accounted for by M, Secchi on the supposition that 
when the ordinary liquid alone is used, there is greater liability to local action 
taking place upon the zinc. In a battery, the circuit of which is closed for 
two minutes every quarter of an hour, M. Secchi has used an ordmary piece 
of commercial sheet-zinc half a millimetre in thickness, which has continued 
in action for more than six months without shovnng the least sign of corro- 
sion. F or large elements, he uses, instead of porous diaphriigms, bags made of 
coarse linen cloth coated with a luting of flour and lime. It is thought 
that these modifications must prove exceedingly useful in practice. 
A Thermo-Spectrometer. — Mr. Crookes, the distinguished editor of the 
Chemical News, makes the following remarks in reference to the propriety of 
devising a new instrument of the above character : Physicists now require an 
apparatus which will enable them to examine and map out the thermal lines 
of the spectrum as accurately as this can be done with the visible or philographie 
portion. With heat radiations of tolerable intensity this would not be difficult 
to effect. A single row of antimony and tellurium bars soldered together at 
their alternate ends, as in the ordmary antimony-bismuth electro-pile, could 
be securely cemented to a solid plate of glass and ground perfectly flat. This 
flat side could then be cemented to a permanent sujjport of glass, ebonite, or 
other non-conducting material of a suitable nature, and the other side (after 
removal of the temporary glass support) should be likewise ground down, till 
the series of bars was no thicker than a card. This side should now be ce- 
mented on to the same kind of supporting material as was used for the other 
side, and the whole securely sealed up at the sides, so as to leave only the ends 
exposed. The end of this pile would now be in the form of a very narrow 
line, which might be half an inch or so in length, and would consist of the 
extremities of ten or a dozen couples of antimony and tellurium bars, each 
not longer than a pin. The extremities of this battery being connected with 
a very sensitive galvanometer, the pile, upon being carried along the ultra-end 
of the spectrum, would instantly reveal when a ray of heat shone upon it, by 
a deflection of the needle, and the comparative intensities of the thermic fays 
could at the same time be ascertained by observing the angular distance to 
which the needle was driven. 
Comparison of Tiventy Barometers. — M. Marie Davy communicated a 
note to the Association Scientifique of Paris, at its meeting on the 8th of 
August last, upon twenty aneroid barometers deposited by M. Vaudez at the 
Observatory. Comparisons of the working of these barometers, continued 
for three months, show that they are subject to the influence of temperature 
like the ordinary mercurial instruments, and that in course of time they 
undergo sensible alterations in the positions of their zero. The displacement 
of the zero differs, according to the amount of care bestowed upon the 
construction of the apparatus, from OT to 07 millimetres. In one barometer 
no alteration took place. These alterations indicate the degree of rehance to 
be placed upon the aneroid barometer. For regular and precise observations, 
nothing can replace a good Fortin’s barometer; but for occasional observations, 
such as the determination of altitudes, an aneroid barometer may furnish 
good results, especially when it can be checked by a mercurial barometer. 
For these .purposes, however, the aneroid might, perhaps, be graduated 
arbitrarily, and furnished with a comparative table. — Vide Beader, Sept. 10. 
