102 
POPULAR SCIENCE REVIEW. 
PHYSIOS. 
Determination of the Temperature of Incandescent Bodies by the Spectro- 
scope. — M. Crova contributes a paper to the Comptes Rendus on tbis subject. 
It follows from tbe researches of Draper and Becquerel that when the 
temperature of an incandescent solid increases continuously, the spectrum 
lengthens towards the violet end. The temperature of the luminous source 
can, therefore, be measured (1) by the wave-length of the radiation which 
limits the spectrum towards the violet ; (2) by the position of the thermal 
maximum of the spectrum which approaches nearer to the violet in propor- 
tion as the emission-temperature becomes higher; (3) by means of the 
ratio of the luminous intensity of a determinate radiation X taken in the 
spectrum of the source to the intensity of the same radiation in the spectrum 
of a source of known temperature, compared with the ratio of the luminous 
intensities of another radiation X' in the same two spectra. The last deter- 
minations can be easily effected by means of a spectro-photometer. 
M. Crova has made numerous determinations of the thermal curves of the 
solar spectrum by means of a linear thermo-electric pile and a very sensitive 
galvanometer. These curves were rendered comparable with one another by 
bringing them to the scale of wave-lengths, and reducing, by means of the 
dispersion curve of the prism, the intensities to those which would corre- 
spond to the case of the normal spectrum of constant dispersion. With these 
he compares the spectrum of the electric light, the lime light, and the 
ordinary moderator lamp, always representing by 1000 the intensity 
corresponding to the wave-length 676. Tie states that, the intensity being 
the same in the red for the four spectra, the weakening towards the violet 
varies with each source according to a certain function of the temperature in 
the following order of increase : — Moderator, stearine candle, gas, lime light, 
electric light, and solar light. 
The Experimental Determination of Magnetic Moments in Absolute Measure 
is the subject of the essay to which the Cleland gold medal was awarded. 
Beginning with a notice of Gauss’s experiments on the intensity of the 
earth’s magnetism, it states that no experiments have been published to 
determine the magnetic moments of steel magnets of different temper and 
tempered by different methods, giving information as to the permanence of 
their magnetism after a considerable time. 
A reflecting magnetometer was used, consisting of a small mirror 1 centim. 
in diameter, carrying cemented to its back four small needles about *8 centim. 
long, and suspended by a single silk fibre. Two arms of wood rotate round 
this, their upper sides level with the centre of the mirror, and grooved with a 
V-shaped depression in which the magnet to be tested could be laid. It 
could thus be made to form any angle with the magnetic meridian, and the 
apparatus could be used either on the method of sines or of tangents. The 
image of a fine wire was brought to a focus on a scale of half millimetres placed 
at a distance of a metre from the plane of the mirror. A large number of 
cylindrical steel bars were cut from one piece, and carefully filed to a uniform 
length of 5 centim. About sixty were raised to bright red heat, and 
plunged into water of 15° 0. They were then made up into parcels of 
five and placed in a vessel containing oil. These parcels were removed at 
