134 REPOET— 1892. 



were constructed as legal ohms, hence the values of the resistance given 

 in ohms at temperatures of 14° or 15° are low. The coils in many cases 

 are very nearly legal ohms at the temperatures given, while they will be 

 ohms some 8° or 10° higher. 



In addition to the coils given in the table, four ohm coils constructed 

 by Messrs. Elliott Bros, for the Board of Trade, one of which is to be 

 selected as the legal unit of resistance for the United Kingdom, were 

 tested very carefully. Some fourteen or fifteen comparisons were made 

 for each coil at temperatures between 9° and 18° between June 1891 and 

 January 1892. The coils were compared directly with the B.A. unit 

 ' Flat,' the difference being expressed in terms of the bridge wire ; while 

 in another series of observations a coil of resistance, 100 ohms, was put 

 in multiple arc with the ohm standard and the difference between ' Flat ' 

 and the combination found ; in this case the length of the bridge wire 

 used was small, and the possible error arising from uncertainty as to its 

 exact temperature was avoided. That this error was very small was 

 proved by the fact that the two sets of observations gave practically 

 identical results. The following are the results : — 



Elliott, 261 



EUiott, 262 



EUiott, 263 



Elliott, 264 



In the case of two of the coils, Nos. 261 and 263, there was one 

 observation for each which differed from the value given by the above 

 formula by '00015 ohm, and this was due to the fact that the ends of the 

 coils had got dirty and needed reamalgamation. None of the other 

 errors in the sixty observations exceeded '00008 ohm, and there were 

 only eight which were as great as '00005. Thus the resistances of these 

 coils are known in terms of the B.A. standards to a very high degree of 

 accuracy. 



During the year Messrs. Elliott Bros, have supplied the Committee 

 with two 1-ohm and two 10- ohm standards; the tests of these are in 

 progress ; two 100-ohm standards are on order. Messrs. Nalder Bros, 

 are also constructing some standards. The Fleming biidge belonging to 

 the Association has been put into thorough repair ; the mercury had 

 damaged some of the copper connecting pieces. 



The Secretary and Mr. Skinner have continued during the year their 

 experiments with Clark cells. These have been communicated to the 

 Royal Society, and the paper is being printed in the ' Phil. Trans.' 



They find that the E.M.F. of their standard cell is 1'4342 volt at 

 15° C, while cells set up by Lord Rayleigh in 1883, 1884, Mr. Elder in 

 1886, Mr. Callendar in 1886, Dr. Muirhead in 1890, Dr. Kahle of Berlin, 

 Dr. Schuster, Mr. "Wilberforce, Mr. Griffiths, and themselves in 1891 and 

 1892 agree closely, the variations among them all being very rarely 

 greater than '0005 volt. 



During the Edinburgh meeting the Committee were honoured 

 with the presence of Dr. von Helmholtz, M. Guillaume of Paris, Pro- 

 fessor Carhart of the United States, Dr. Lindeck and Dr. Kahle of the 

 Berlin Reichsanstalt. These gentlemen came by invitation to consider 

 the question of establishing identical electric standards in various 



