[ald] 
XI. A Determination of the Specific Heat of Water in Terms of the International 
Electric Units. 
By Artaur Scuuster, /.R.S., Langworthy Professor of Physics at the Owens College, 
Manchester, and Witu1aM Gannon, M.A., Exhibition (1851) Scholar, Queen’s 
College, Galway. 
Received November 13,—Read November 22, 1894. 
Tuts research was originally undertaken by Professor ScoustErR and Mr. H. Hapiey 
before the authors were aware that Mr. E. H. Grirriras was engaged on a similar 
investigation. After a number of preliminary experiments, and just as the final 
arrangements for the conduct of the measurements were being definitely made, 
Mr. Haptey, 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 mechanical 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 may be obtained at present. 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. Hapiey’s departure, Mr. W. Gannon took his place. 
From the former gentleman we received a good deal of help in the devising 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 [EC dt, where E is the difference of 
potential at the ends of the conductor, C the current and ¢ the time, we keep the 
electromotive force constant, and measure (c dt 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 are able to complete the experiment more quickly than 
19.7.95. 
