SCIENTIFIC SUMMARY. 
227 
sucli portraits from time to time, and we have seen various specimens of 
their handiwork. Of all the carte ” portraits, however, which have come 
under our notice, those which have been taken hj Mr. Philip Crellin strike 
us as infinitely the best, both in point of photographic excellence and from 
their wonderfully truthful expression of feature. Among the instances 
especially worthy of notice we would call attention to the portraits of Pro- 
fessor Huxley, Sir Henry Thompson, Hr. Odling, and Professor W. A. Miller, 
which are extremely life-like, and — by no means a usual quality in -^photos ” 
— perfectly natural in pose. 
PHYSICS. 
A Neio Galvanic Battery., which promises to be an extremely useful 
instrument both to the physicist and the therapeutist, has been recently 
brought under the notice of the Chemical Society by Mr. He la Rue and Hr. 
Hugo Muller. The following account of it is given by a contemporary : — 
The negative plate is of chloride of silver, and the positive plate of zinc, 
the exciting fluid being salt and water. The one exhibited was of very 
small size, yet gave indications of considerable intensity. The chloride of 
silver is fused around a thin silver wire as the negative element, the positive 
plate being composed of a small rod of zinc which need not be amalgamated. 
The size of the whole arrangement does not exceed three inches in height, 
and, with a battery of ten cells excited with salt water, a rapid current of 
mixed oxygen and hydrogen gases was evolved from acidulated water. 
When in use the salt brine becomes gradually charged with chloride of 
zinc, which tends to increase the energy of the battery, the whole arrange- 
ment continues in working order until metallic zinc begins to be deposited 
on the negative element, when the exciting liquid must be changed. For 
" convenience of putting the whole series at once into action, the round bars 
of zinc and chloride of silver are fastened at the top to a wooden frame, 
which is made to slide upon glass uprights ; when immersed, the chloride of 
silver undergoes a slow reduction to metallic silver, and this permeates the 
mass, producing an appearance like virgin arborescent silver. 
The Law of the Production of the Electric Light. — A paper on this subject 
has been written by Prof. Edlund, and read before the Royal Society of 
Stockholm. The voltaic current is capable of conversion into several varie- 
ties of force, and among the number into heat. The heat produced by such 
a current is proportional to the square of the intensity of the current multi- 
plied by the resistance. The entire quantity of heat generated is propor- 
tional consequently to the electro-motive force divided by the resistance of 
the current, and this sequence holds so long as the current performs no other 
work except the generation of heat alone. In the luminous arc which con- 
stitutes the electric light, material particles are detached by the current 
from one pole and transferred to the other, and by the mechanical disintegra- 
tion of the poles an electro-motive force is produced which sends a current 
in an opposite direction to that of the principal current. The electro-motive 
force in the luminous arc is independent of the intensity of the current, and 
