224 LORD RAYLEIGH AND PROFESSOR W. RAMSAY ON ARGON, 
occurs at 603°84. A group of five bright green lines occurs next, besides a number of 
less intensity. Of this group of five, the second, which is perhaps the most brilliant, 
has the wave-length 56100. There is next a blue, or blue-violet, line of wave-length 
470°2 and last, in the less easily visible part of the spectrum, there are five strong 
violet lines, of which the fourth, which is the most brilliant, has the wave- 
length 420°0. 
Unfortunately, the red lines, which are not to be mistaken for those of any other 
substance, are only to be seen at atmospheric pressure when a very powerful jar- 
discharge is passed through argon. The spectrum, seen under these conditions, has 
been examined by Professor ScousteR. ‘he most characteristic lines are perhaps 
those in the neighbourhood of F, and are very easily seen if there be not too much 
nitrogen, in spite of the presence of some oxygen and water-vapour. The approximate 
waye-lengths are :— 
ASE 5 a BAN RORIYES, 
(A86:07)" oe ee DY 
A84-71 . . . . . Not quite so strong. 
AGO 32) re ee Strona? 
476°50 | 
473°53 . . . . Fairly strong characteristic triplet. 
472°56 | 
It is necessary to anticipate Mr. CrooksEs’s communication, and to state that when 
the current is passed from the induction-coil in one direction, that end of the capillary 
tube next the positive pole appears of a redder, and that next the negative of a bluer 
hue. There are, in effect, two spectra, which Mr, Crooxess has succeeded in separat- 
ing to a considerable extent. Mr. E. C. C. Baty,* who has noticed a similar phe- 
nomenon, attributes it to the presence of two gases. The conclusion would follow that 
what we have termed “ argon ” is in reality a mixture of two gases which have as yet 
not been separated. This conclusion, if true, is of great importance, and experiments 
are now in progress to test it by the use of other physical methods. . The full bearing 
of this possibility will appear later. 
A comparison was made of the spectrum seen in a vacuum tube with the spectrum 
in a “plenum” tube, 7z.e., one filled at atmospheric pressure. Both spectra were 
thrown into a field at the same time. It was evident that they were identical, 
although the relative strengths of the lines were not always the same. The seventeen 
most striking lines were absolutely coincident. 
The presence of a small quantity of nitrogen interferes greatly with the argon 
spectrum. But we have found that in a tube with platinum electrodes, after the 
* *Proe. Phys. Soc.,’ 1893, p. 147. He says: ‘‘ When an electric current is passed through a mixture 
of two gases, one is separated from the other, and appears in the negative glow.” 
