320 
POPULAR SCIENCE REVIEW. 
light, he is inclined to infer that the property, so far from being exceptional, 
is one enjoyed in greater or less measure by all metals. In the case of 
selenium and tellurium, it has been suggested that the alteration of resist- 
ance is due to the action of calorific rather than of luminous rays. But no 
such objection can be urged against the experiments with the noble metals. 
In fact, the resistance of these metals increases with the temperature , so that 
when it is found that on exposure to direct light the resistance is dimi- 
nished, it is clear that heat can have nothing tc do with causing such a 
change. Heat, indeed, tends to mask the effects of light, and the diminu- 
tion of resistance is therefore a differential effect ; an effect representing the 
difference between the increase of resistance consequent on rise of tempera- 
ture, and the decrease of resistance due to the action of light. Dr. Born- 
stein’s experiments, therefore, show beyond question that the electric con- 
ductivity of the noble metals is exalted, or their resistance diminished, by 
the direct effect of luminous rays. 
The Electric Candle. — Experiments have been recently conducted at the 
West India Docks with the view of testing the illuminating power of the 
so-called electric candle devised by M. Paul Jablochkoff. This simple means 
of producing a steady electric light consists in placing two carbon pencils 
side by side, but separated by a bar of a composition called u kaolin.” On 
the passage of the current the carbons slowly burn down, and the kaolin is 
consumed by the heat at exactly the same rate. The carbons are thus kept 
always at the same distance apart, and the light playing between them is 
thus rendered constant without the aid of complex regulators. In the ex- 
periments at the West India Docks the current was produced by a magneto- 
electric machine, worked by a small steam-engine, and the results are de- 
scribed as having been eminently satisfactory. For lights of small and 
medium size, an apparatus of even greater simplicity may be employed, the 
carbon points being dispensed with and nothing used beyond a piece of 
the so-called kaolin held between the electrodes. But M. Jablochkoff’s 
prime improvement, which promises to greatly extend the use of the electric 
light, consists in his ability to divide the current, so as to supply several 
-candles placed in the same circuit, each with its own coil. These candles 
may be of various degrees of illuminating power, and may be lighted or 
extinguished separately. In short, the electricity appears to be under such 
control, that it might be generated in some central establishment and laid 
on through wires to the several centres of illumination, just as freely as 
gas is at present distributed through pipes to any number of burners. MM. 
Denayrouze and Jablochkoff, who have employed the light in Paris, have 
described their process before the French Academy of Sciences. — Comptes 
rendus, No. 16, April 17, 1877. 
Magnetization of Polarized Light. — It was Faraday who first showed, by a 
series of famous experiments, that magnetism is capable of exerting a re- 
markable influence on light which has undergone that physical change 
which is called polarization. When a beam of plane-polarized light is 
transmitted through certain transparent media placed between the poles of 
an electro-magnet, the plane of polarization is rotated in this direction or 
in that, according to the course which the electrical current is caused to 
take in circulating through the coils of the magnet. Dr. J. Kerr, of Glas- 
