444 POPULAR LECTURES AND ADDRESSES. 



President how very much more accurate were 

 the measurements of resistance in the practical 

 telegraphy of Dr. Werner Siemens and his 

 brother, our President, than in any laboratory 

 of theoretical science. Whilst in the laboratory 

 of theoretical science it had not been discovered 

 that the [conductivity of different specimens of 

 copper differed at all, in practical telegraphy 

 workshops they had been found to differ by from 

 thirty to forty per cent. When differences 

 amounting to so much were overlooked when 

 their very existence was not known to scientific 

 electricians the great founders of accurate 

 measurement in telegraphy were establishing 

 standards of electric resistance accurate to one- 

 tenth per cent. Dr. Werner Siemens and our 

 President were among the first to give accurate 

 standards of resistance, and the very first to give 

 an accurate system of units founded upon those 

 standards. The Siemens unit is still well known, 

 and many of the most important measurements 

 in connection with submarine cables are stated 

 in terms of that unit. By a coincidence, which 



