32 REPORTS ON THE STATE OF SCIENCfi. 



will suttlc in u defuiito luauuei- the few luatters relating to the fuudd- 

 inental units which are still outstanding, and will organise a method 

 whereby a close agreement may be maintained among the electrical 

 standards in use throughout the world. 



The electrical measurements of certain of the fundamental units, 

 which have been in progress for some time at the National Physical 

 Laboratory, have been brought to a conclusion, and the results 

 publislied in three papers in the ' Philosophical Transactions ' of the 

 Royal Society. 



1. 'A New Current Weigher and a Determination of the Electromotive Force 

 oE tlie Normal Weston Cadmium Cell.' By Professor W. E. Ayrton, F.R.S., and T. 

 Mather, F.R.S., Central Technical College, London; and F. B. Smith, A.R.C.Sc, 

 National Physical Laboratory, Teddington, Phil. Trans., A, vol. 207, pp. 463-549. 



2. ' On the Normal Weston Cadmium Cell.' By F. E. Smith, Phil. Trans., A, 

 vol. 207, pp. 393-420. 



3. ' On a Comparison of many forms of Silver Voltameters.' By F. E. Smith ; 

 and ' A Determination of the Electrochemical Equivalent of Silver.' By F. E. Smith 

 and T. Mather, F.R.S., Phil. Trans., A, vol. 207, pp. 545-58L 



' The Chemistry of the Silver Voltameter.' By F. E. Smith and T. M. 

 Lowry, D.Sc, Phil. Trans., A, vol. 207, pp. 581-599. 



From the first of these it appears that to a very high degree of 

 accuracy the electromotive force of the Weston cadmium cell, as set up 

 at the National Physical Laboratory, when expressed in terms of the 

 ampere (10"^ C.G.S. units of current) and the international ohm is 

 l-018.3o at a temperature of 17° C. 



The second Paper deals with the preparation of the Weston cadmium 

 cell, and contains a comparison between cells set up at the Laboratory 

 and others constructed elsewhere, the general conclusion being that cells 

 can be nrepared by different persons in different countries which will 

 agree in'E.M.F. to 1 or 2 parts in 100,000. 



In the third Paper there is given an account of a comparison of some 

 six forms of silver voltameters, and it is shown that the silver deposited 

 by a current of one ampere in all these various forms is the same if 

 proper precautions are taken, and amounts to 



1 •11827 milligramme per second. 



After this work was completed a comparison was made by Messrs. 

 T. Mather and F. E. Smith, by tlie kindness of Mr. Trotter, between the 

 ampere standard of the Board of Trade and the ampere as realised by the 

 new Ayrton Jones balance at the National Physical Laboratory. The 

 comparison, an account of which appears in the ' Proceedings of tlic 

 Royal Society,' A, vol. 80, 1908, was very satisfactory. 



It was found that the Board of Trade ampere will deposit silver at the 

 rate of I'll 79, milligramme per second, a value which is nearly identical 

 with the number 1*1179^ given by Lord Rayleigh and Mrs. Sidgwick in 

 1884. Indirectly the E.M.F. of the normal Weston cadmium cell was 

 found to be 1-01879 Board of Trade volts at 17° C, the Board of Trade 

 volt being defined as the potential difference between the terminals of a 

 resistance of 1 Board of Trade ohm when 1 Board of Trade ampere is 

 passing through it. 



During the year the ten mercury standards at the National Physical 

 Laboratory have again been set up and intercompared. An account of 

 this work appears in an Appendix by Mr. F. E. Smith, the value 

 vf the international ohm, as realised by the mean of the ten tubes, l^eing 



