The author has observed a fact which furnishes a remarkable demonstration
of the law of the production of the dark bands which he has detected in
the spectrum of oxygen. The phenomena of elective absorption in oxygen gas
are manifested in two mutually distinct spectral systems. A first system,
formed of fine rays, follows the law of the product of the gaseous system
traversed by its density. The second system is formed of bands much less
easily resolved, is governed by the law of the product of the thickness by
the square of the density. This second law being quite novel in spectral
analysis, the author has instituted experiments necessary to prove that
this system of obscure bands really belongs to oxygen. These experiments
range from pressures of 100 atmospheres down to those of a few units, and
with lengths of tubes from 0.42 meter to 60 meters. At the same time
prolonged observations have been made upon the atmosphere, brought into
connection with the experiments in the tubes. These observations, and
especially those made during autumn last on the Pic du Midi, prove that
all the bands of the spectrum of oxygen are found in the spectrum of the
solar light if it is allowed to traverse a sufficient thickness of the
atmospheric medium. Further, on comparing, by the aid of photography, the
intensities of the bands of the atmospheric spectrum with those given in
the tubes, the author has found that the intensities of these atmospheric
bands fulfill the law of the square. It appears from _Wiedemann's Annalen_
that M. Olszewski, when liquefying oxygen, examined its spectrum and
ascertained the existence of the bands in question with a stratum of 7 mm.
of liquid oxygen.--_J. Jansen._
ON A THEORY CONCERNING THE SUDDEN LOSS OF MAGNETIC PROPERTIES
OF IRON AND NICKEL.
By Mr. H. TOMLINSON, B.A.
Experiments by himself and other observers have shown that the
temperatures at which iron and nickel lose their magnetic properties
depend on the specimens used and the magnetizing forces employed; but the
temperatures at which they _begin to lose_ these properties are
definite--for nickel about 300 deg. C., and iron about 680 deg. C. The author's
own experiments on "Recalescence of Iron" show two critical temperatures;
and Pinchon has shown by calorimetric measurement that between 660 deg. and
720 deg. C., and between 1,000 deg. and 1,050 deg. C., heat becomes latent. All these
facts seem to indicate a molecular rearrangement about these temperatures.
In his proposed theory he assumes that the molecules of iron (say)
contain magnetic atoms capable of motions of translation and of rotation.
These tend to form closed magnetic circuits, but at ordinary temperatures
are unable to do so on account of the close proximity of their centers. On
raising the temperature their centers are further separated, till at about
680 deg. C. their polar extremities rush together, forming complete circuits
and exhibiting no external magnetic properties. On cooling down, the
centers approach until the gravitation attraction overcomes the magnetic
attraction of their poles, when the magnetic properties reappear.
Prof. Ayrton asked whether the author had made experiments on the
reappearance of magnetic properties when raised to a white heat, and Prof.
Thompson inquired whether cobalt had been tested. Both questions were
answered negatively.