A NEW CONSTITUENT OF THE ATMOSPHERE. 229 
SS AL, If e C, 
nh =o = ak at) — ? 
where 7 is the frequency, \ is the wave-length of sound, v its velocity, e the 
isothermal elasticity, d the density, (1 + at) the temperature-correction, C, the 
specific heat at constant pressure, and C, that at constant volume. In comparing 
two gases at the same temperature, each of which obeys Bovte’s law with sufficient 
approximation and in using the same sound, many of these factors disappear, and the 
ratio of specific heats of one gas may be deduced from that of the other, if known, 
by the simple proportion 
NAG 2 NEG 8 BPE} S aa, 
where for example \ and d refer to air, of which the ratio is 1°408, according to 
the mean of observations by ROnTGEN (1°4053), WULLNER (1°4053), Kayser (1°4106), 
and JAMIN and RicHaRD (1°41). 
The apparatus employed, although in principle the same as that usually employed, 
differed somewhat from the ordinary pattern, inasmuch as the tube was a narrow one, 
of 2 millims. bore, and the vibrator consisted of a glass rod, sealed into one end of 
the tube, so that about 15 centims. projected outside the tube, while 15 centims. was 
contained in the tube. By rubbing the projecting part longitudinally with a rag wet 
with alcohol, vibrations of exceedingly high pitch of the gas contained in the tube 
took place, causing waves which registered their nodes by the usual device of 
lycopodium powder. The temperature was that of the atmosphere and varied little 
from 17°5°; the pressure was also atmospheric, and varied only one millim. during 
the experiments. Much of the success of these experiments depends on so adjusting 
the length of the tube as to secure a good echo, else the wave-heaps are indistinct. 
But this is easily secured by attaching to its open end a piece of thick-walled india- 
rubber tubing, which can be closed by a clip at a spot which is found experimentally 
to produce good heaps at the nodes. 
The accuracy of this instrument has frequently been tested ; but fresh experiments 
were made with air, carbon dioxide, and hydrogen, so as to make certain that 
reasonably reliable results were obtainable. Of these an account is here given. 





| | | | | 
| Number of observations. Half-wave-length. | 
Gas in tube. |— - | Ratio 4 : 
| | £7) | 
| I, | II. | I, II. | | 
| | | | 
Air. 3 2 19°60 19°59 1-408 Assumed | 
CO;. 3 1511 Oo | 1:276 Found 
125 ee 3 73°6 50 | 1376 Found 

To compare these results with those of previous observers, the following numbers 
