SCIENTIFIC SUMMAKT. 
103 
is made a series of recesses to fit the cells and keep tliem in their places. 
This base rests on feet of vulcanite to increase the insulation. The zincs 
pass through holes in the bar and are kept in position by vulcanised collars. 
Above these collars another on each zinc serves as a clip for making con- 
nection with the silver wires, which is done by passing the wire between 
the zinc and the collar. The silver wires pass through holes pierced in 
pieces of gutta-percha or ebonite, fitted into the mahogany bar, the holes 
being only just large enough to permit of the wire being drawn through 
them. The zincs are better amalgamated, but need not be so. The cells 
are charged with a solution of salt in distilled water, 25 grammes to the litre. 
When the chlorine is more or less completely exhausted by the reduction of 
the cylinders through their entire thickness, the resulting rods of spongy 
silver can be renewed and reconverted into chloride with scarcely any loss of 
silver, so that the cost of the renewal of the battery is chiefly one of labour. 
The inventors find that their battery has about the same electro-motive force 
as Daniel’s battery. They also give experiments showing the constancy of 
the battery. 
TAe delation of Mechanical Strain of Iron to Magneto-electric Induction,-^ 
Mr. G. Gore has established, by means of an apparatus he describes in the 
Philosophical Magazine for December, that a magnetised soft iron wire during 
the ^ct of being stretched (either with temporary or permanent elongation) 
increases in magnetism and produces in a coil of insulated copper wire sur- 
rounding it, a current of electricity in a contrary direction to that of the 
hands of a watch when we are looking towards its south pole. 
A Molecular Change in Tin produced hy Cold . — At St. Petersburg last 
winter, according to Herr Fritsche, tin exposed to a temperature of 40° 
below zero, was converted into a semicrystalliue mass, containing cavities 
like basalt. Some of these cavities in masses of 25 or 30 kilos, of tin had 
a volume of 100 cubic centimeters. According to M. Dumas facts of this 
kind were not new in Russia in one case the organ pipes in a church were 
so altered by the cold as to be no longer sonorous. The fracture of axles by 
cold is perhaps a fact of the same nature. — Comptes-Pendus, Nov. 30. 
A New Method of measuring the Intensity of Light . — A simple instrument 
for this purpose has been devised by Mr. Roger Wright, and has been recently 
described in the Proceedings of the Royal Society, for measuring approxi- 
mately the intensity of total daylight for comparative purposes. It consists 
of a solid rod of metal standing perpendicularly on a heavy base. The top 
of the cylinder is painted white vdth a black spot in the centre. A hollow 
tube blackened inside is made to fit exactly and slide over this rod. The rod 
is marked with a scale, beginning with zero at the base. To use the instru- 
ment, the tube is pushed over the rod down to the zero-point j it is then 
drawn slowly up, the observer looking steadily at the black spot, and when 
the spot vanishes in the gloom, the point is read off* on the graduated scale. 
This point will, of course, vary with the intensity of the light, and thus a 
measure of the intensity is obtained. 
A Neiv Differential Refractor for Polarised Light. — M. Jamin has de- 
scribed to the French Academy an instrument adapted to all the purposes 
of his differential refractor for ordinary light, by which polarised light may 
be employed instead. 
