176 
DR. E. P. PERMAM, DR. W RAMSAY, AND MR. J. ROSE-INNES, 
Stronger note, capable of leaving a distinct trace upon the wax ; the experiment was 
also repeated with a shorter tube. The following results were obtained ;— 
Length. 
i 
1 
No. of points in 
one revolution. 
millims. 
Tube No. 1 
. . 1.5.5-59 
766 1 
„ 2 . 
. . 100-0-2 
1190 
' 
A tuning-fork, of frequency 1024, was found to leave 232 imjiressions in one revo¬ 
lution. This gives as the velocity of sound in tins particular kind of glass 263,000 
and 262,700 centims. per second for the two tubes respectively. 
We may take the mean, 262,850 centims. per second, as the velocity of sound in 
the glass rod, and this assumption, though we have no guarantee of its exact truth, 
is unlikely to introduce any serious error. We then find that a rod 28'3 centims. 
long will emit 18,578 vibrations per second, and this number may be accepted as 
giving roughly the frequency of the glass rod when performing free vibrations. In 
the actual apparatus used, the rod was sealed on to a glass tube, near its middle, and 
this may well have had the effect upon it of a rider on a tuning-fork, and lowered the 
tone. The test in the present case is, therefore, only a rough one, but it has some 
value all the same, as it shows that the dust-heaps observed in all these experiments 
were really due to the vibrations of the fundamental note in air, and not to the 
higher harmonics in the glass. 
It was decided upon the whole to adopt the value of 7i, derived from the experi¬ 
ments with air, as there is less manipulation required in this case, and, therefore, less 
liability to experimental error. By comparing the experiments with air, hydrogen, 
and argon, it will be seen that the value of the frequency is uncertain, to an extent 
of about I per cent. ; but it will be shown later on that the particular manner in 
which this constant enters into the equations renders the uncertainty of far less 
importance than might [it first appear. 
IV. Calculations of the Adiabatic Elasticity. 
Having ascertained the volume of 1 grm. corresponding to each pressure and 
temperature observed, and having also found the corresponding mean wave-lengths, 
the velocity of sound in the ether-gas was calculated by the formula — 
V = nX, 
where V is velocity, n the number of vibrations per second, 17,56(), and X the wave¬ 
length. The following results were obtiiined : — 
