1864. | Physics. 503 
ing that a bundle of rays having a section of a square inch, would in 
one minute raise the temperature of a cubic inch of water by 0°733 of a 
degree centigrade. On comparing these results with those of Pouillet, it 
is seen that the latter observer found the heat of the sun’s rays to be one- 
eighth less. Pouillet, however, assumed that the height of the earth’s 
atmosphere was jequal to the 80th part of the earth’s radius, whilst 
M. Hagen finds that the height of the atmosphere, assuming that the 
layers of air have the same power of absorption, is only equal to the 
178rd part of the earth’s radius. 
In his remarkable work on heat considered as a mode of motion, 
Dr. Tyndall observed that it would be interesting to see whether the 
balls of rifled guns would not show signs of fusion. M. Schroeder 
remarks, that, by having a ball constructed of zine, he thinks it would 
be possible to estimate the amount of heat given out on striking the 
target. He finds that at a temperature above boiling water zinc be- 
comes granular, and that if the heat is very gradually increased, the 
metal will, without losing its form, assume exactly the appearance of 
zinc that has been melted. It is not unlikely that an experiment with 
this metal might furnish some information, but the determinations of 
temperature would not be very accurate, and it would probably be 
possible to discover a more certain way of estimating the heat given 
out by the concussion ; at the same time the suggestion is useful in 
the absence of a better measure of temperature under the conditions of 
the experiment. 
Dr. Tyndall has been for some time past engaged in some investi- 
gations on the non-luminous heat-rays of the spectrum with reference 
to their deportment towards certain bodies which are perfectly opaque 
to light. He has found that a solution of iodine in bisulphide of 
carbon entirely intercepts the light of the most brilliant flames, whilst 
to the ultra red rays of the spectrum the same solution is perfectly 
diathermic. Ifa hollow prism is filled with this opaque liquid and 
placed in the path of the beam from an electric lamp, the light-spec- 
trum will be completely intercepted, whilst the heat-spectrum passes 
through, and can be examined by a thermo-electric pile. A liquid of 
this kind, which will allow physicists to sift the heat-rays from the 
light-rays, will be of great value in many experiments in physical 
optics. Indeed, the discoverer is not the person to allow such a 
valuable adjunct to experiment to remain idle in his hands. 
It has long been known that heat weakens or destroys the mag- 
netic force in permanent magnets, but we are not aware that any very 
accurate researches have been made on this subject. M. Mauritius 
has lately published* some results, in which he shows that when a 
permanent magnet is alternately exposed to the temperatures 100° C. 
and 0° C., the magnetism ultimately becomes sensibly constant on 
the return of the same temperature. It is now found that when the 
magnetism at 0° and then the magnetism at 100° are measured, a dimi- 
nution takes place at the higher temperature and a corresponding 
* «Bibliotheque Universelle de Geneve,’ March, 1864. 
