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POPULAR SCIENCE REVIEW. 
along a wire, that this latter becomes elongated to a greater extent than 
would he explained by the increase of temperature in the wire. This is his 
mode of experimenting : — Taking a wire the amount of whose expansion by 
heat is known with perfect exactitude, a current is passed through, and the 
elongation of the wire is measured ; if its temperature at the moment be 
known, it will be seen whether its elongation is in accordance with this 
temperature, or is greater. In order to estimate the temperature, M. Edlund 
measures the electric conductivity of the wire, and having arrived at this he 
deduces the temperature from it. This process of investigation always 
proves that the temperature is lower than would explain the elongation of 
the wire. Hence he concludes that the elongation is not the result of heat. 
It must therefore be produced by the passing currrent. — Vide PoggendorfF s 
Annalen , No. 9. 
The Physics of the Fire-damp Indicator. — One of the latest forms of Mr. 
Ansell’s Fire-damp Indicator is thus described by a contemporary : — It con- 
sists of an iron funnel, provided with an iron U-tube, the end of which is 
closed by a piece of glass tube, fixed in brass, to which one pole of a battery 
is attached ; the upper part of this glass tube carries a brass collar, through 
which passes an adjusting screw, to the lower end of which is fastened a 
piece of copper wire with a platinum point. Mercury is poured into the iron 
funnel till it rises in the glass tube to a convenient height. This mercury is 
allowed to find its level by the opening of a valve, when setting the instru- 
ment. The septum is a tile of Wedgwood’s ware, and closes the open part 
of the funnel, good sealing wax being the best cement for securing it in its 
place. The other battery wire is connected with the instrument, so that, if 
diffusion take place, the mercury is pressed up against the platinum point, 
and thus communication is established. Mr. Ansell has found that this in- 
strument gives warning in four seconds, if the mixture of gas be still below 
the point of explosion ; but, by adjusting the point so that there is not more 
than the thickness of a shilling between it and the mercury, a dangerous 
irruption may make itself known in two seconds. 
A Cheap and Ingenious Ice Machine. — M. Tonelli, says the Abbe Moigno 
has just devised an ice-making machine which bids fair to become very 
popular in this country, since it is convenient, cheap, and efficient. The 
inventor calls it the “ glacier roulante .” It is a simple metallic cylinder 
mounted on a foot. The salt of soda and the salt of ammonia are added 
in two operations, the smaller cylinder containing the water to be frozen 
is introduced into the interior, and the orifice is closed by an india- 
rubber disc, and then by a cover fastened with a catch ; the cylinder is 
then placed in a sac, or case of cloth, and it is made to roll on the table 
with a slight oscillatory movement given by the hand. After a lapse of 
ten minutes, the water in the interior of the cylinder becomes a beautiful 
cylinder of ice. Nothing is more simple, more economical, or more effica- 
cious than the new u glacier roulante ,” which costs 10 fr., and gives us, 
moreover, what could not hitherto be obtained with an apparatus containing 
freezing mixtures — the means of freezing a decanter of water or a bottle of 
champagne. The apparatus, in a case, packed for travelling, with 20 
kilogrammes of refrigerating materials and a measure, costs, at present, 
only 1/. 
