128 Progress in Science. [January, 
simple and unlikely to get out of order. A battery of two carbon cells 
per mile will work the instrument. 
M. F. M. Raoult has lately submitted to the Academy of Sciences the 
result of his researches on the calorific coefficient of the hydro-eleGric and 
thermo-electric currents. The law he deduces is—that the heat evolved by an 
electric current is independent of the nature of the galvanic element, the 
calorific coefficient, Ke, being the same for all sources of galvanic (current) 
electricity. 
Count du Moncel has recently published, in the ‘Bulletin de la Société 
d’Encouragement pour l’Industrie Nationale,” an interesting report on the 
bichromate of potash battery, in which he states the following conclusions :-— 
Of all the galvanic elements used in industry and the arts, those with 
bichromate of potash yield the greatest eleftro-motive force, are the most 
economical, and give off no irritating vapours, but are, on the other hand, not 
very constant and become strongly polarised. These effects are less marked 
in the Delaurier element with two liquids, and are also greatly obviated in the 
Chutaux element with a constant discharge; the use of the Chutaux element 
with sand and constant discharge offers peculiar advantages in every respect 
for electric telegraphy and all similar applications, because this element is for 
equal force more economical than the Daniell element. The Delaurierelement 
with two liquids may be advantageously used instead of the Bunsen element 
when strong electric currents are required. In order to obtain a continuous 
and energetic action with the bichromate of potash battery, the most effectual 
method is the application of a current of air, as invented by M. Grenet. By 
the addition of bisulphate of mercury to the bichromate solution in the Chutaux 
element a very continuous and energetic electric current may be obtained. 
Dr. Alvergniat has described some new phenomena of phosphorescence 
produced by frictional electricity. A vacuum is first made in glass tubes 
about 45 centimetres in length. After the introduction into these tubes of a 
small quantity of either chloride or bromide of silicium, the pressure inside 
these tubes having been reduced to 12 or 15 millims., they are sealed before the 
blowpipe. When such tubes are rubbed with a piece of silk, there appears 
inside the tubes a bright luminous flash, which exhibits a rose colour with the 
chloride, and a yellowish-green colour with the bromide, of silicium. Only 
when a more perfect vacuum is made in these tubes the induction spark 
produces a luminous phenomenon in them, but,then the phosphorescence by 
friction entirely disappears. 
All draughtsmen are acquainted with the simple device of puncturing holes 
through a drawing for the purpose of obtaining an outline and afterwards 
transferring the outline by sifting fine plumbago or other powder through the 
small holes. The fatigue of making the holes by hand is very great, and 
M. Cauderay, of Lausanne, proposes to employ the induction coil for this 
purpose. A table covered with tinfoil is connected with the negative pole; on 
it may be placed as many sheets of paper as the spark will pass through. 
The positive pole, consisting of a metal bar, insulated with gutta-percha, can 
serve as a pencil for copying the tracings. The metal point of the pencil 
being moved about on the contour and outline of the engraving, electric sparks 
spring across every time a connection is made, and puncture fine holes through 
the paper. It is said to require little skill to guide the pencil, as the ink 
tracings being good condué¢tors, carry the pencil easily along. In the case of 
valuable engravings it is better to make a copy with the pantagraph and use 
that for the punching process. The pantagraph is connected with the positive 
pole of the induction apparatus, and it is placed upon a table, one-half of 
which is covered with tin-foil, The drawing to be copied lies upon the 
insulated half, and the sheets of paper to be punctured are laid upon the tin- 
foil. The pointer of the pantagraph moves around the outlines of the 
engraving, and between the pen and the foil the sparks pass to pierce the paper 
upon which the outline is tobe made. In this way the engraving or original 
drawing is in no way injured. ‘ 
