~~. os 
Dec. 21, 1882] 
NATURE 
183 
Pror, MELDE of Marburg proposes to study the force of 
electric reaction as exhibited in the rotation of Hamilton’s well- 
known ‘‘mill,” by attaching the ‘‘ mill” to a torsion fibre, and 
observing the ovgue produced by the electric reaction. As 
Tomlinson has shown, the ‘‘mill” will work when surrounded 
by turpentine or other insulating liquid ; hence Prof, Melde’s 
suggestion promises to prove of some interest. 
Dr. H. P. Bowpircu has recently published in the ournal 
of Physiology a paper on the optical illusions of motion, in 
which he deals chiefly with the peculiar illusions of rotation, 
&c., studied a few years ago by Prof. Silvanus P. Thompson. 
He entirely agrees with the latter experimenter in rejecting the 
explanation advanced by R. Addams, and more recently by 
Javal, that these illusions are due to muscular slip, and declares 
that such an explanation is worthless, being contradicted by the 
fact that motor after-effects in opposite directions are possible 
for the same retina at the same time. Dr. Bowditch also thinks 
that these persistent after-impressions of motion cannot be the 
product of experience or association, because experience cannot 
overcome, nor volition control or reverse them. He looks for 
an explanation in the narrowness of the limits of distinct vision, 
M. Berson has contributed to our knowledge of the magnetic 
properties of metals by some recent researches on their degree 
of magnetisation at different temperatures. The experimental 
method followed consisted in comparing the magnetic moments 
of different bars by Gauss’s method at different temperatures 
while placed in a magnetic field of constant intensity. The fol- 
lowing are the results :—With iron the total and temporary 
magnetisations both increase up to 260° C., above which the 
temporary magnetisation falls off rapidly, but the permanent 
slowly. In steel the total magnetisation is also a maximum at 
260° C., but the permanent magnetisation attains its maximum 
about 240°C. The magnetisation of a steel bar magnetised 
while cold is diminished by heating, whilst that of a bar mag- 
netised while hot is diminished by cooling. This result appears 
to be important, as it would follow that a magnct has its perma- 
nent maximum power at that temperature at which it was mag- 
netised, With nickel the total magnetisation increases up to 
240°, and diminishes above 280° so rapidly as to be zero at 
330°. But if magnetised at 280°, the magnetic moment during 
the subsequent cooling first increases, then diminishes slightly, 
but still remains greater than at the temperature at which it was 
magnetised. Cobalt behaves like steel. 
M. HEsEHUs publishes in the last volume of the ¥ournal of 
the Russian Chemical and Physical Society an interesting paper 
on his researches on “ residual elasticity ” (a rather difficult term 
to translate), the e/astische Nachwirkung of W. Weber. With- 
out attempting to deal with the immense range of phenomena 
concerning permanent changes of shape of elastic bodies under 
the influence of small but continually acting forces, M. Hesehus 
has studied these changes in a few bodies, especially in lead and 
caoutchouc, and has made an attempt to bring these changes 
into connection with other physical phenomena. He comes to 
the conclusion that residual elasticity depends to a great extent 
upon the mass of the body, and its surface; that the elastic con- 
ductibility depends upon, and increases with, temperature ; and 
that the laws of residual elasticity afford close analogies with 
those of heating and cooling of solid bodies, as well as with 
those of phosphorescence and of residual magnetism and 
electricity. 
AT a meeting of the Russian Physical Society, M. Kraevitch 
made an interesting communication on the results of his re- 
searches on the elasticity of air, Narified air does not obey the 
Boyle-Mariotte law, that is, in proportion as it becomes more 
rarified its elasticity diminishes more rapidly than its density, 
and becomes equal to zero, while the density has stiil a measur- 
able value. M. Kraevitch observes that it would result from 
these experiments: (1) that the atmosphere of the earth is 
limited ; and (2) that our weights of gases contain an error, as, 
however perfect the pneumatic machine, it cannot pump all air 
from a vessel, if this vessel is lower than the pneumatic machine, 
or the air is pumped from above. Prof. Mendeleeff, recognising 
the importance of these researches, advised M. Kraeyvitch to 
continue them on heavy gases. 
{In a paper relating to recent studies of the Rhone glacier 
(read at last meeting of the Helvetic Society of Sciences), Prof. 
Forel formulates these four questions as, in his opinion, the 
most urgent for a theoretic knowledge of the phenomena of 
glaciers : (1) How and in what measure does the velocity of 
flow vary in different layers of the depth of the glacier? (2) 
How and in what proportion does the surface-velocity vary if 
the glacier increases or diminishes in thickness? (3) What is 
the temperature of the internal mass of the glacier? (4) What 
are the laws of periodic variations of different glaciers? (For 
this study it is desirable to know, in the case of each glacier, 
the epochs of commencement of ; periods of elongation or 
shortening). 
HERR Herz has recently measured with special apparatus, 
the pressure of saturating vapour of mercury at different tempe- 
ratures, from 0° to 220° (Wied. Ann., No, 10). His numbers 
are considerably smaller than those of Regnault ; and with Herr 
Hagen’s they agree only between 80° and 100° C., being greater 
below, and smaller above these limits. Between o° and 40° he 
finds the elastic force of the vapour of mercury to vary from 
0'00019 mm. to 00063 mm. It follows that at ordinary atmo- 
spheric temperatures it is less than y~;5 mm. This result is 
important in reference to barometers, machines, and Geissler 
tubes. 
S1GNor Martini has studied the sounds produced by outflow 
of water through a cylindrical hole in a metal disc at the bottom 
of along glass tube filled with the liquid (A/¢i del. R. Lst. Veneto, 
5 ser. t. viii. 1882), In such a case one does not hear a series of 
sounds of decreasing pitch, though the liquid charge continually 
shortens ; but a certain number of distinct sounds. The sound 
is due, as Savart proved, to the vibrations of the liquid vein ; 
and the author verified Savart’s law, that the numbers of these 
are proportional to the liquid charge and inversely as the 
diameter of the hole. A pure sound of clear tonality is only 
got if the sound of the vein is one of those the liquid column 
can yield. The series of sounds from a liquid column of con- 
stant length is that of the harmonics of an open pipe. The air 
column above the liquid strengthens some of the sounds. The 
sound is quenched if the tube is kept from vibrating. These 
experiments afford a means of comparing the velocities of sounds 
in different liquids. One has only to find what lengths the 
columns must have to yield a particular sound (all air-bubbles 
must be expelled), The author has tried alcohol, sulphuric 
ether, and petroleum, and found numbers agreeing with those by 
other methods. 
Ir appears from recent experiments by Herr E. Wied- 
mann (Wied. Ann., No. 12) that a number of water-contain- 
ing salts, when heated, undergo chemical transposition even 
before fusion. He has, in this inquiry, found two new modifica- 
tions of zinc-sulphate and magnesium-sulphate, and determined 
the changes of volume attending their formation. The general 
result, he ‘points out, is of interest with reference (1) to deter- 
mination of tension, inasmuch as it is necessary, first, to ascer- 
tain whether a given salt remains unaltered or not within the 
range of temperature considered ; (2) to researches on heat of 
solution, &c., of a salt partly deprived of water by heating ; it 
should be exactly determined in what form water and anhydride 
salt are combined. 
CHEMICAL NOTES 
A RECENT patent by Mr. Morris, of Uddingston, N.B., claims 
to have solved a problem which has long baffled the skill- of 
technical chemists. By heating an intimate mixture of alumina 
and charcoal, in a current of carbon dioxide, Mr. Morris says 
that metallic aluminium is produced ; the metal is purified from 
carbon and aluminium by fusion. 
WHAT may perhaps be called the kinetic theory of chemical 
actions, the theory, namely, that the direction and the amount 
of any chemical change is conditioned not only by the affini- 
ties, but also by the masses of the reacting substances, by the 
temperature, pressure, and other physical circumstances—is 
being gradually accepted, and illustrated by experimental results. 
Thus Hammond (M@onatsheft fiir Chimie, 3, 149) concludes, 
from experiments on the hydration of salts, that when a saline 
solution is gradually concentrated various hydrates are formed, 
but that the crystallisation of any one of these from the liquid 
depends on the relative quantities of the various hydrates, and on 
the temperature of the solution, Another example of the esta- 
blishment of a state of equilibrium between antagonistic chemical 
systems is furnished by the recent observations of L. de Bois- 
baudran (Compt. rend., 95, 18) on gallium protochloride. When 
gallium is dissolved in cold concentrated hydrochloric acid a 
