ON THE ADIABATIC RELATIONS OF ETHYL OXIDE. 
181 
But, on the whole, the resulting curves show good concordance. Where a number of 
curves such as these, differing from each other by regular intervals, is drawn, the 
position of each of them lends control to that of its neighbour, and a close approxi¬ 
mation to accuracy may be deduced from very unpromising material.'" 
These curves were then further utilized by reading off the values of for equal 
volumes, 70, 65, 60, and so on, at intervals of 5 down to volume 20 cub. centims. per 
grm., and at smaller intervals, viz., 17’5, 15, 14, 13 cub. centims. per grin., and so on, 
down to 4 cub. centims. per grm. at smaller volumes. 
From these numbers a second diagram was constructed, representing the values of 
\^]v plotted againsb temjDerature, the^lines being isochoric. These curves were 
observed not greatly to deviate from straight lines—:they intersected at small 
volumes. They would probably also intersect at larger volumes if produced.. It has 
not been thought necessary to reproduce this figure as it is virtually contained in 
fig- 4. 
The value of V'Vt’ is, of course, the same as the adiabatic elasticity, .and, like the 
isothermal elasticity, it has the dimensions of a pressure. It will be remembered 
that V was measured in centimetres per second, and v in cub. centims. per grm. 
Consequently, the elasticity, as calculated above, must be given in absolute units, or 
dynes per sq. centirn. It was found more convenient to change to pressures measured 
in millimetres of mercury, and this can be readily done by dividing all the foi’mer 
numbers by 1384’2. 
V. Mathematical Discussion of Preceding Kesults. 
We noticed above that for equal volumes the adiabatic elasticity is roughly a linear 
function of the temperature, and this fact seems to hold out some hope of bringing 
all the experimental results obtained under the power of analysis. An inspection 
of the diagram shows that the difference between the isochorals actually drawn and 
straight lines is no greater than the uncertainty due to experimental errors, so that 
as far as the direct evidence goes it is possible that the isochorals are really straight. 
Even if it should turn out on subsequent investigation that the isochorals are slightly 
curved, the treating them as straight lines may be considered as a first approximation 
to the truth, and as a justifiable simplification of a very complex problem. 
Let us call the adiabatic elasticity measured in millimetres of mercury E, then we 
may put 
E = ./T - h, 
where g and h are functions of the volume only. Now, it was shown by one of the 
authors, in conjunction with Dr. Sydney Young, that for constant volumes there is a 
* The cnrve.s actually given in fig. 4 have been calculated by meaius of the formula on p. 183; they 
are the smoothed version of a set of similar curves drawn to represent the actual observations. They 
agree with the observations better than the original free-hand curves. 
