THE spectrum exhibited by argon undoubtedly shows that, under the conditions of the experiment, the molecules composing the gas are set into an intense state of vibration, while the ratio of the specific heats (5/3, about) shows, according to the equation, β = I/γ – I, that β = I, and therefore the gas is, as pointed out by Lord Rayleigh, monatomic, and cannot therefore be capable of vibrating. But there is, I think, a very simple explanation of this apparent contradiction, and that is, that the above equation is not true, and that it should be, as will be proved hereafter, β = 3k(γ – I), where k is very nearly 1 for argon and other so-called permanent gases. This latter equation gives 2 for the value of β in argon, a value easily understood.