SEPTEMBER 1, 1899. ] 
SPREADING AND REVERSAL OF SPECTRAL 
LINES. 
WANNER, Wied. Ann. 68, p. 143, 1899, de- 
scribes the change of the sodium spectrum when 
the light from the flame is repeatedly reflected 
back and forth through the flame. He finds a 
spreading of the D lines, accompanied by a 
sharply defined reversal, and a weak continu- 
ous spectrum in their neighborhood. 
W. Voigt, Wied. Ann. 68, p. 604, shows that 
this observation of Wanner is in qualitative ac- 
cord with his theory of the emission of a 
layer of gas, which theory shows that in the 
radiation from a thin layer the wave-length 
which would be most absorbed would be of 
maximum intensity ; while the radiation from a 
very thick layer would give a continuous spec- 
trum with a dark absorption line; that is, a re- 
versal of the original spectral line. 
LECTURE EXPERIMENTS WITH THE WEHNELT 
INTERRUPTER. 
E. LECHER, Wied. Ann. 68, p. 623, 1899, de- 
scribes some very beautiful experiments show- 
ing the action of a magnetic field upon the 
electric discharge from an induction coil using 
a Wehnelt interrupter. The experiments illus- 
trate the well-known sidewise movement of the 
spark (are) across the magnetic field. The high 
frequency obtained with the Wehnelt inter- 
rupter, together with the fact that the discharge 
approaches the character of an arc, makes the 
effect of the magnetic field most striking in ap- 
pearance; and the author describes several 
arrangements of the apparatus well suited to 
lecture-room demonstration. 
VELOCITY OF ELECTRIC WAVES IN AIR. 
‘Mr. G. V. MACLEAN describes, in Phil. Mag., 
July, 1899, a very successful application of the 
coherer in the location of the modes and anti- 
nodes of a stationary electric wave train re- 
flected from a metal sheet. Mr. Maclean’s 
object was to determine the velocity of the 
waves from the observed wave-length and the 
periodic time of the oscillator. 
The coherers used consisted essentially of two 
platinum globules which were adjusted to 
delicate contact, and a milliamperemeter in 
circuit with the coherer and a battery gave the 
SCIENCE. 299 
indications. The coherer gave no response at 
all at the nodes, and the readings over more 
than a whole wave of the stationary train were 
remarkably regular considering the erratic 
space action of the ordinary form of the coherer. 
W'S. HB. 
NOTES ON INORGANIC CHEMISTRY. 
THE great problem in obtaining argon from 
the atmosphere is to remove the nitrogen. In 
the earlier experiments, asin that of Cavendish, 
the electric discharge was passed through air 
confined over potash, whereby the nitrogen is 
gradually oxidized and absorbed. Later it 
was found that nitrogen was absorbed directly 
by various metals with different degrees of 
rapidity. Magnesium was first used by Ramsay, 
and somewhat later Ouvrard used. lithium, 
while more recently Maquenne’s mixture of 
magnesium with lime has been found practically 
most efficient. A very thorough study of the 
different absorbents has been made by Hempel, 
in the Zeitschrift fiir anorganische Chemie. »He 
finds that lithium is five times as efficient as 
magnesium, the magnesium-lime mixture eight 
times, while if to a mixture of one part mag- 
nesium dust with five parts lime a quarter part 
of sodium is added, this absorbent is no less 
than twenty times as rapid in its action as 
magnesium alone. 
THE early experiments of Professor Berthelot 
on the absorption of argon by organic com- 
pounds under the prolonged action of the silent 
discharge have now been very largely ex- 
tended, and are described in the Comptes Rendus. 
With quite a large number of compounds of the 
fatty series, such as ethylene, aldehyde, ace- 
tone, propionitril, the result was negative. On 
the other hand, with benzene, turpentine, 
phenol, benzaldehyde, benzonitril and quite a 
number of other compounds of the benzene se- 
ries from one to six per cent. of argon was ab- 
sorbed, and at the same time there was a 
fluorescence of greenish color and with a char- 
acteristic spectrum. 
In the same number of the Comptes Rendus 
there is an interesting observation by M. Ches- 
nan to the effect that chromous salts, like 
ferrous, have the property of absorbing nitric 
oxid. The compound formed, however, is 
