A NEW CONSTITUENT OF THE ATMOSPHERE. 235 
Fifth: It is in the highest degree improbable that two processes, so different from 
each other, should each manufacture the same product. The explanation is simple if 
it be granted that these processes merely eliminate nitrogen from “ atmospheric 
nitrogen.” 
Sixth: If the newly discovered gas were not in the atmosphere, the discrepancies 
in the density of “chemical” and “atmospheric” nitrogen would remain unexplained. 
Seventh: It has been shown that pure nitrogen, prepared from its compounds, 
leaves a negligible residue when caused to enter into combination with oxygen or 
with magnesium. 
There are other lines of argument which suggest themselves; but we think that it 
will be acknowledged that those given above are sufficient to establish the existence 
of argon in the atmosphere. 
It is practically certain that the argon prepared by means of electric sparking with 
- oxygen is identical with argon prepared by means of magnesium. The samples have 
in common :— 
First : Spectra which have been found by Mr. Crookes, Professor ScHuUSTER, and 
ourselves to be practically identical. 
Second: They have approximately the same density. The density of argon, pre- 
pared by means of magnesium, was 19°9; that of argon, from sparking with oxygen, 
about 19°7 ; these numbers are practically identical. 
Third: Their solubility in water is the same. 
That argon is an element, or a mixture of elements, may be inferred from the 
observations of § 14. For Ciausius has shown that if K be the energy of translatory 
motion of the molecules of a gas, and H their whole kinetic energy, then 
Kee BCR = Oo) 
H 2C, Q 

CU, and C, denoting as usual the specific heat at constant pressure and at constant 
volume respectively. Hence, if, as for mercury vapour and for argon (§ 14), the 
ratio of specific heats C, : C, be 13, it follows that K = H, or that the whole kinetic 
energy of the gas is accounted tor by the translatory motion of its molecules. In the 
case of mercury the absence of interatomic energy is regarded as proof of the mon- 
atomic character of the vapour, and the conclusion holds equally good for argon. 
The only alternative is to suppose that if argon molecules are di- or polyatomic, 
the atoms acquire no relative motion, even of rotation, a conclusion improbable in 
itself and one postulating the sphericity of such complex groups of atoms. 
Now a monatomic gas can be only an element, or a mixture of elements; and 
hence it follows that argon is not of a compound nature. 
According to AvoGaDRo, equal volumes of gases at the same temperature and 
pressure, contain equal numbers of molecules. The molecule of hydrogen gas, the 
density of which is taken as unity, is supposed to consist of two atoms. Its mole- 
7 Wa, 
