1864. | Physics. 699 
of an hour and allowed to cool, were found to have their specific 
gravities diminished respectively to 2°978, 2°980, and 2-977. In 
one month’s time the specific gravities, upon being again determined, 
were found to have risen to 3-844, 3°350, and 3°345. The author 
considers it probable that this property will be found to belong more 
or less to all substances without exception. 
It has become an important desideratum for physicists engaged 
in the investigation of the spectrum lines to be in possession of an 
instrument which will readily reveal the presence of fixed lines in the 
heat-spectrum. The ordinary form of thermo-electric battery is in- 
applicable for this purpose on account of its shape, besides being 
scarcely delicate enough for rays of feeble intensity. Mr. Crookes 
has proposed a method of forming a thermo-spectrometer, which will 
enable physicists to examine and map out the thermal lines of the 
spectrum as accurately as this can be done with the visible and photo- 
eraphie portion. Instead of using antimony and bismuth bars, it is 
proposed to use the far more powerful combination of antimony and 
tellurium. A single row of these bars are soldered together at their 
alternate ends, and, after being cemented to a temporary but rigid 
flat surface, the series is ground perfectly flat. This flat side is then 
cemented to a permanent support of glass, porcelain, ebonite, or other 
suitable non-conducting material, and the other side (after removal of 
the temporary supporting-surface) is likewise ground down until the 
series of bars is no thicker than a card. This side is now cemented to 
the same kind of supporting material as was used for the other side, and 
the whole is firmly and securely sealed up, so as to leave only the ends 
exposed. The end of the pile now appears in the form of a very 
narrow, slightly-disconnected line, half-an-inch or so in length, and 
consisting of the extremities of ten or a dozen couples of antimony 
and tellurium bars, each not larger than a pin. By connecting the 
extremities of this pile with a sensitive galvanometer, and carrying it 
along the ultra-red end of the spectrum, keeping the line of extremities 
parallel with the fixed spectrum lines, it will instantly reveal when a 
ray of heat shines upon it by a deflection of the needle; and the 
comparative intensities of the thermic rays can be at the same time 
ascertained by recording the angular distance to which the needle is 
deflected. 
Execrriciry.—Although not able to record any striking discovery 
in electrical science which has taken place during the last quarter, we 
have noted several ingenious applications of this force, as well as 
improvements in instruments connected with it. A suggestion of - 
M. Dufour for preventing the explosion of steam-boilers is especially 
worthy of notice for its ingenuity, as well as for the important results 
which would attend its successful adoption. Mr. Grove has shown 
that when water is deprived of the air naturally dissolved in it, and 
is then heated, it does not boil steadily at any fixed temperature; the 
temperature rises many degrees above the normal boiling-point, and the 
liquid then suddenly bursts into tumultuous ebullition ; it now remains 
quiet for a short time whilst the temperature is again accumulating, 
and the same phenomena are again repeated, increasing in violence 
