IV. Appendix to a communication entitled 'the mechanical equivalent of heat'

In a communication which I had the honour of making to the Royal Society in the spring of this year, the following statement occurs (p. 420):—“We are (with the help of Mr. Callendar) now entering on a careful direct comparison of thermometer Em 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.” A great number of comparisons have been made during the summer of this year by Mr. Callendar and myself between the mercury thermometer Em used by me for determining the temperature of the calorimeter, the Tonnelot thermometer, No. 11,048, described in the above paper (pp. 426—433), the platinum thermometer N, by which the mercury thermometer Em had been previously standardised, and two air thermometers constructed by Hicks under Mr. Callendar’s direction.