420 
MK. E. H. GRIFFITHS OH THE VALUE OF 
Section X. —The Measueement of Temperatuee. 
When commencing this account of our experiments, we proposed to give full details 
of the calibration and standardization of the mercury thermometer E,«, upon which all 
our measurements depend. Nearly half of our time and attention has been devoted 
to this part of the subject, and there are but two courses open to us, viz,, to give a 
full account of our method of standardization, with the tables upon which oui’ con¬ 
clusions are based ; or to reserve a detailed description for a further communication, 
and give a short summary of the results in the present paper. We have decided to 
adopt the latter course, for the following reasons :— 
(1.) We are (with the help of Mr. Callendar) now entering on a careful direct 
comparison of thermometer E,„ with a new form of air thermometer, which, there is 
every reason to believe, will give very accurate results; but we are unable to assign 
any definite limit to the time that this investigation may take. 
(2.) Dr. Guillaume is now”' engaged in the comparison with the Paris standard of 
a thermometer specially constructed for us by M. Tonnelot, and some time must 
elajise before this comparison can be completed. 
(3.) The dimensions of this communication are already very great, and if, in addi¬ 
tion, we gave a full account of our thermometric comparisons, its length would become 
immoderate. 
(4.) We consider that the success of the method of exact determination of tem¬ 
perature by platinum thermometers may now be regarded as established, and that the 
accuracy of the results obtained by platinum thermometers in our possession is proved 
by communications already published.! 
(5.) The results of our J experiments may themselves be taken as a proof of the 
accuracy of the method of time-calibration adopted by us, and described on pp. 423 
and 424, infra. 
Assuming the accuracy of the calibration it is possible we are in error— 
(1.) In the actual elevation ; , 
(2.) In the value of our total range. 
No. (1) may be disregarded, for it is only the changes in the specific heat of water 
which render the actual elevation of any consequence whatever. Now it is impossible 
that we are in error by 0°*2 C., for the comparisons we have made with the B.A. 
thermometers, which have been carefully standardized at Kew, would alone have 
been sufficient to detect an}^ error of that kind, and an error of 0°‘2 C. in elevation 
would mean an alteration of only 1 in 20,000 in the value of J. 
No. (2) is, of course, of vital importance. 
In ‘ Pliil. Trans.,’ vol. 182, A, p. 155, will be found the results of a comparison of one 
* December, 1892. 
t ‘B.A. Report,’ 1890; ‘Phil. Trans.,’ vol. 182, A, pp. 43-72 and 119-157; ‘Phil. Mag.,’ December, 
1891; ‘ Chem. Soc. Journ.,’ 1890, p. 656. 
