710 



SCIENCE. 



[N. S. Vol. I. No. 26. 



a characteristic group. He also placed 

 upon the sketch some of the lines of zinc, 

 which were verj^ convenient as dii-ecting 

 one exactly where to look. (See Fig.) 



Within the last few days Mr. Crookes 

 has charged a radiometer with argon. 

 When held in the light from the electric 

 lamp the vanes revolve rapidly. Argon is 

 anomalous in many respects, but not, you 

 see, in this. 



Next, as to the density of argon. Pro- 

 fessor Eamsay has made numerous and care- 

 ful observations upon the density of the gas 

 prepared by the magnesium method, and he 

 finds a density of about 19.9 as comxjared 



the density of a gas, and also the velocitj^ 

 of sound in it, we are in a position to infer 

 this ratio of specific heats ; and by means 

 of this method. Professor Eamsaj^ has de- 

 termined the ratio in the case of argon, 

 arriving at the verj^ remarkable result that 

 the ratio of specific heats is represented bj^ 

 the number 1.65, approaching very closely 

 to the theoretical limit, 1.67. The number 

 1.67 would indicate that the gas has no 

 energy except energy of ti-anslation of its 

 molecules. If there is any other energy 

 than that, it would show itself by this num- 

 ber dropping below 1.67. Ordinary gases, 

 oxygen, nitrogen, hydi-ogen, etc., do di-op 



43 44 45 46 47 48 49 SOOO 



je. 



^yon 



Med 



J^^ 



abydr 



II Y 



with hydrogen. Equally satisfactory obser- 

 vations upon the gas derived by the oxygen 

 method have not yet been made, but there 

 is no reason to suppose that the densitj^ is 

 different, such numbers as 19.7 having been 

 obtained. 



One of the most interesting matters in 

 connection with argon, however, is what is 

 known as the ratio of the specific heats. I 

 .must not stay to elaborate the questions in- 

 volved, but it will be known to many who 

 hear me that the velocity^ of sound in a gas 

 depends upon the ratio of two specific heats 

 — ^the specific heat of the gas measured at 

 constant pressure, and the specific heat 

 measured at constant volume. If we know 



below, giving the number l.-i. Other gases 

 drop lower still. If the ratio of specific 

 heats is 1.65, practicallj^ 1.67, we may infer 

 then that the whole energy of motion is 

 translational ; and from that it would seem 

 to foUow hj arguments which, however, I 

 must not stop to elaborate, that the gas 

 must be of the kind called by chemists 

 monatomic. 



I had intended to say something of the 

 operation of determining the ratio of specific 

 heats, but time wUl not allow. The result 

 is, no doubt, very awkward. Indeed, I 

 have seen some indications that the anoma- 

 lous properties of argon are brought as a 

 kind of accusation against us. But we had 



