48 Prof. H. L. Callendar on the T Jiermodynamical 



between the observed and calculated values of the deflexion is 

 therefore as good as could be expected. 



My chief object in setting up the apparatus with the magnetic 

 needle was to test experimentally certain criticisms made in 

 my former paper on M. Cremieu's experiments, especially 

 his experiments on open electric circuits *. However, in 

 consequence of unavoidable delays, it was not until the 1st of 

 June that I was ready to proceed with the work. But now 

 the damp and sultry weather of the summer had set in and put 

 an end to all experiments with static electricity for the time 

 being. 



I wish here to express my thanks to Prof. Ames of the 

 Johns Hopkins University, to whose kindness I am indebted 

 for the opportunity of carrying out these experiments, and 

 whose criticisms and suggestions have proved of great value. 



Baltimore, Md., July 1, 1902. 



III. On the Thermodynamical Correction of the Gas-Ther- 

 mometer. By H. L. Callendar, M.A., F.R.S., Professor 

 of Physics, Royal College of Science j\ 



1. Introduction. 



nPHE correction of the gas-thermometer to the absolute 

 X scale is a subject possessing considerable theoretical 

 interest ; it has also acquired some practical importance at 

 the present time in view of the increasing accuracy attainable 

 in thermometric measurements. A number of papers on the 

 subject have recently appeared in the Philosophical Magazine 

 and other periodicals. These show some divergence in the 

 methods proposed and in the results deduced, and little has 

 yet been done in the direction of calculating tables of cor- 

 rections for different gases, or in the practical application of 

 the results to thermometric measurements. 



I propose in the present paper to give some account of the 

 theoretical and experimental work bearing on the subject ; 

 to explain a method of expression in terms of the " Co-aggre- 

 gation Volume " which I have found very convenient in 

 treating similar problems relating to imperfect gases ; and to 

 show how to calculate tables of corrections in a simple and 

 practical manner. 



* Comptes Rendus, cxxxii. p. 1108. 



t Communicated by the Physical Society. Read March 26th, 1901. 

 Publication was delayed to await the results of experiments in progress 

 at University College. But in consequence of my removal to the Royal 

 College of Science, it has been found impossible to include this experi- 

 mental work in the present paper. 



