1894.] Specific Heat of Water in Electric Units. 



I. " A Determination of the Specific Heat of Water in terms of 

 the International Electric Units." By ARTHUR SCHUSTER, 

 F.R.S., Langworthy Professor of Physics at the Owens 

 College, Manchester, and WILLIAM GANNON, M.A., Exhibi- 

 tion (1851) Scholar, Queen's College. Galway. Received 

 November 13, 1894. 



(Abstract.) 



This research was originally undertaken by Professor Schuster and 

 Mr. H. Hadley, before the authors were aware that Mr. E. H. Griffiths 

 was engaged on a similar investigation. After a number of pre- 

 liminary experiments, and just as the final arrangements for the 

 conduct of the measurements were being definitely made, Mr. 

 Hadley, on his appointment to the Head Mastership of the School 

 of Science and Art, Kidderminster, had to leave Manchester. In 

 the meantime Mr. Griffiths' important research was published, and 

 we had to consider whether our own work, which was designed on a 

 smaller scale, could compete with it in accuracy. We decided to 

 complete the investigation, principally for the reason that, although 

 we both aimed at determining what is commonly called the mechani- 

 cal equivalent of heat through the heating of a certain mass of water 

 by means of an electric current, the details of the experiments 

 differed very materially, so that our two ways of dealing with the 

 problem seemed to afford a useful test of the amount of agreement 

 which at present may be obtained. Our investigation touches only a 

 small part of that treated by Mr. Griffiths, as we did not attempt to 

 measure the changes in the specific heat of water due to change of 

 temperature. On the other hand, the more modest limits within 

 which we have confined ourselves allowed us to use a much simpler 

 apparatus. 



On Mr. Hadley 's departure, Mr. W. Gannon took his place. From, 

 the former gentleman we received a good deal of help in the divising 

 and construction of some important parts of the apparatus. 



The principle of the method we have used is extremely simple. 

 The electrical work done in a conductor being measured by J ECcfa, 

 where E is the difference of potential at the ends of the conductor, 

 C the current, and t the time. We keep the electromotive force con- 

 stant, and measure f Cdt directly by a silver voltameter. We do not, 

 therefore, require to know the resistance of the wire, and we thus 

 avoid the difficulty of having to estimate the excess of temperature 

 of the wire over that of the water in which it is placed. We also 

 gain the advantage of not having to measure time, and therefore of 

 being able to complete the experiments mere quickly than we could 



