THE MECHANICAL EQUIVALENT OF HEAT. 
431 
It thus appears that our temperatures, as deduced by platinum thermometers, 
exceed those of the Paris Hydrogen and Nitrogen Standards in actual elevation by 
0°'014 C. and 0°'005 C. respectively, but that the value of our total temperature range 
is practically the same by both methods of standardization.* 
It is true that slight discrepancies appear in the value of the smaller ranges, but 
here I am inclined to place greater reliance on our previous determinations than on 
those obtained by the comparison with P, for mistakes of observation are far less 
likely to occur when using platinum, than when reading mercury, thermometers, and 
also the former values are deduced from the observation of several different resist¬ 
ances at each temperature, all of which after the correction given by the standardization 
of the resistance-box (see p. 408, supra) are in practical agreement, although the ' 
actual values of P differ greatly. 
The difference in actual elevation is of no consequence, although it is interesting 
to notice that the agreement with the Paris Nitrogen Scale is nearer than that with 
the Hydrogen Scale. This was to be expected, since the boiling-point of sulphur 
was ascertained by Mr. Callendae, and myself by means of an air thermometer, and 
our values of d depend on that determination. 
We have not, as yet, been able to commence, by means of Mr. Callendar’s new 
form of air thermometer, our direct comparison with the nitrogen scale, for the 
calibrating and cleaning of the instrument have occupied much time. Pending the 
completion of that work the results of the above comparison are of great value, and, 
in the meantime, we are justified in assuming that the temperature range values, as 
determined by us, are in such close agreement with the Paris nitrogen thermometer 
as to render any alteration in our results unnecessary. The reduction of our tempe¬ 
rature from the air, to the absolute, scale would diminish the value of our total 
temperature range by nearly ’002, but I do not consider the accuracy of our results 
of such an order as to render the resulting correction (about 1 in 5000) more than a 
matter of form. 
I have forwarded this note to Dr. Guillaume with the request that he would be 
so good as to add his opinion as to the probable limit of error of the observations 
with thermometer P, together with any other comments which he may think advis¬ 
able. His remarks are as follows :— 
“ Le resultat fort remarquable des comparaisons faites par M. Griffiths est sans 
doute le mellleur criterium de la limite d’erreur, tant des observations du thermo¬ 
metre que de son etude ; et I’estimation que j’en aurais faite d priori aurait ete 
sensiblement plus elevee. En effet, dans le rdsultat final viennent s’ajouter toutes les 
causes d’erreurs suivantes :— 
* The ranp^e value on the corrected mercury scale is (in the case of this thermometer) II 508, and this 
would diminish our value of J by 1 part in 367. 
