230 LORD RAYLEIGH AND PROFESSOR W. RAMSAY ON ARGON, 
were obtained for carbon dioxide :—Cazin, 1:291; ROnTGEN, 1°305; De Luccut, 
1:292; MULLER, 1:265; WULLNER, 1°311; DuLonc, 1°339; Masson, 1:°274; Rec- 
NAULT, 1°268; AMAGAT, 1:299 ; and JAMIN and RicHaRD, 1:29. It appears just to 
reject DuLone’s number, which deviates so markedly from the rest; the mean of 
those remaining is 1°288, which is in sufficient agreement with that given above. 
For the ratio of the specific heats of hydrogen, we have :—Cazin, 1:410; RontcEn, 
1°385 ; Dutone, 1'407; Masson, 1°401; REeGNAULT, 1°400; and Jamin and RicHarp, 
1:410. The mean of these numbers is 1°402. This number appears to differ con- 
siderably from the one given above. But it must be noted, first, that the wave- 
length which should have been found is 74°5, a number differing but little from that 
actually found ; second, that the waves were long and that the nodes were somewhat 
difficult to place exactly ; and third, that the atomic weight of hydrogen has been 
taken as unity, whereas it is more likely to be 1°01, if oxygen, as was done, be taken 
as 16. The atomic weight 1°01 raises the found value of the ratio to 1°399, a number 
differing but little from the mean value found by other observers. 
Having thus established the trustworthiness of the method, we proceed to describe 
our experiments with argon. 
Five series of measurements were made with the sample of gas of density 19°82. 
It will be remembered that a previous determination with the same gas gave as its 
density 19°90. The mean of these two numbers was therefore taken as correct, 
viz., 19°86. 
The individual measurements are :— 



| ih | IL. | Ws) jf? | V. Mean. | 
| bi i | | 
| millims. 
| 18:16 1814 1802 | 1804 18:03 18:08 
| | 

for the half-wave-length. Calculating the ratio of the specific heats, the number 
1°644 is obtained. 
The narrowness of the tube employed in these experiments might perhaps raise a 
doubt regarding the accuracy of the measurements, for it is conceivable that in 
so narrow a tube the viscosity of the gas might affect the results. We therefore 
repeated the experiments, using a tube of 8 millims. internal diameter. 
The mean of eleven readings with air, at 18°, gave a half-wave-length of 
34°62 millims. With argon in the same tube, and at the same temperature, the 
half-wave-length was, as a mean of six concordant readings, 31°64 millims. The 
density of this sample of argon, which had been transferred from a water gas-holder 
to a mercury gas-holder, was 19°82; and there is some reason to suspect the presence 
of a trace of air, for it had been standing for some time. 
The result, however, substantially proves that the ratio previously found was 
