20 Mr. W. M. Mordey on the Dynamo 



volt, which becomes ( — TTTTT — = ) "318 vo ^, allowing for 



difference of standard. 



In reference to a point to which these authors* drew 

 attention a short time ago, namely, that, although the heat 

 evolved by displacing cadmium by zinc in solutions *25 

 CdCl 2 , 100 H 2 is greater than that evolved by the same 

 substitution in the case of the sulphates, yet the E.M.F. of 

 the zinc-cadmium chloride cell is materially less than that of 

 the zinc-cadmium sulphate cell, my measurements afford direct 

 confirmation, as the value given here for the average E.M.F. 

 of the zinc-cadmium sulphate cell is '335 volt and that for the 

 zinc-cadmium chloride cell only *301 volt, or a difference of 

 *034 volt, substantially the same as the difference given by 

 them, viz. *035. 



III. Electromotive Force of Zinc- Tin Iodide Cell. 



A cell set up with amalgamated zinc in *25 Znl 2 , 100 H 2 

 opposed to tin in '25 Snl 2 , 100 H 2 0, both solutions acidified 

 with 1*5 per cent, of HI, was found to have an E.M.F. of from 

 •47 to -49, averaging *485 volt. 



There being no thermal data at my disposal no comparisons 

 can be drawn. 



IV. The Dynamo as a Generator and as a Motor. Some 

 Analogies and Contrasts. By W. M. Moedey, Esq.} 



DUBINGr the last few years an immense amount of atten- 

 tion has been given to everything relating to theory 

 and practice of dynamo machines. So thorough has been the 

 study of the problems connected with these machines, which 

 are of a character to appeal both to the physicist and the 

 practical constructor or engineer, that it is now not difficult to 

 lay down, in a fairly complete form, the laws governing their 

 action, and the rules and principles under which they should be 

 constructed ; although three or four years ago much confusion 

 and uncertainty existed as to what was best in dynamo 

 construction. 



But in electric motors the case is very different. While it 

 is easy to name physicists and constructors in considerable 



* Phil. Mag. vol. xvii. p. 378 (May 1884). 

 t C ommunicated by tlie Author. 



