the Thermodynamic Scale of Temperature. 315 
Conclusion. 
We have found that there is a good agreement between 
the two estimates of the freezing-point which are given in 
the present part of this paper, and are derived from the 
experimental data concerning hydrogen and nitrogen re- 
spectively ; the closeness of this agreement entitles us to 
consider the present method as superior in accuracy to those 
previously employed. Vse may also place considerable con- 
fidence in the tables of thermodynamic corrections given in 
this paper ; because, as has been already pointed out, while 
we confine ourselves within the limits of temperature and 
pressure, within which the Joule-Thomson effect has been 
observed, the precise algebraic form of the expression chosen 
to represent the effect has practically no influence on the final 
numerical results. Bat outside these limits the algebraic 
form of the expression chosen to represent the Joule-Thomson 
effect may, and in general will, exercise considerable influence 
on the final numerical results. For this reason I have not 
given the thermodynamic correction for temperatures lying 
either below the freezing-point or above the boiling-point. 
And until we know the true form which ought to be emploved 
for the Joule-Thomson effect, the results of calculating the 
thermodynamic corrections for such temperatures must be 
largely speculative. 
The above considerations point to a large gap in our 
knowledge, and some physicists have endeavoured to meet 
the difficulty by employing a rational formula for the Joule- 
Thomson effect based upon some molecular hypothesis 
regarding the constitution of gases. The drawback to such 
a method of procedure is that the trustworthiness of the final 
numerical results is made to depend not merely on the two 
laws of Thermodynamics and on data derived from experi- 
ment, but also on the truth or falsehood of a speculative 
hypothesis. The introduction of such speculations into the 
treatment of a purely thermodynamic question must be 
considered as being to a large extent a step backwards. On 
the other hand, it is not possible to remain contented with the 
present state of our knowledge of the thermodynamic 
correction to a gas-thermometer ; we have to confine our 
theory to temperatures which lie between the boiling- and 
freezing-points, or which are but slightly removed from 
those limits. 
The most simple and at the same time the most effective 
method of meeting the difficulty would be to repeat the 
Joule-Thomson experiments over a much wider range of 
