348 Professor Arthur Schustpr [May 18, 



a series of international metric standards. Bv a convention, entered 

 into by the different countries at a diplomatic conference held at Paris 

 in March and April 1875, means "were created for carrying out the 

 work of verifying standards under a new International Metric Com- 

 mittee, and for the purpose of enabling the Committee to execute their 

 duties effectually, as well as of securing the future custody and preserva- 

 tion of new metric prototypes and instruments, the Permanent Metric 

 Bureau was founded. The original cost of the Bureau was 20,000/., 

 and the annual budget was fixed at 3000/. for the period during 

 which the prototypes were being prepared, after which time it was 

 expected that the expenditure could be reduced to 2000/. In 1901, 

 however, it reached 4000/., the maximum to which by the terms of the 

 convention the annual budget could be raised. Great Britain did not 

 join the convention until 1884, when it declared its adhesion. A first 

 payment of 1787/. was made as entrance fee, and the annual contribu- 

 tion now ranges between 200/. and 300/. Major MacMahon, to whom 

 I owe the above details, is at present the British representative on the 

 International Committee. 



The work can-ied out at Sevres is not confined to the reproduction 

 of metric standards, butmeasurementsof precision in various directions 

 have been made with conspicuous success. Scientific thermometry 

 owes much to the International Bureau, and in some respects it may 

 be said that exact thermometry was created there. Professor 

 Michelson's work in which the length of the metre was compared 

 directly with the length of a wave of red light, is another classical 

 investigation carried on in the laboratories of the International 

 Bureau. More recently Mr. Guillaume examined the physical properties 

 of alloys, notably those of nickel steel, and proved the possibility of 

 manufacturing a material which shows no sensible expansion with rise 

 of temperature. The importance of metallic rods the length of which 

 does not depend on temperature is obvious, provided they prove to be 

 of sufficient permanence. 



It would lead me too far if I were to give an account of the 

 Conference and Conventions which have led to a general agreement on 

 the standards of electric measurements, but it is a satisfaction to 

 know that these standards are essentially those proposed and first 

 constructed by the British Association. The old British Association 

 ohm no doubt was found to be wrong by more than 1 per cent, but 

 it has remained the prototype of the present international unit, and in 

 principle the old ohm, volt, and unit of current stand as they were 

 given to us by the original Committee.* 



* The original Committee was appointed in 18G1, and consisted of : Pro- 

 fessors A. Williamson, C. Wheatstone, W. Thomson (Lord Kelvin), W. H. Miller, 

 Dr. A. Matthiessen, and Mr. P. Jenkins. In the following year, Messrs. 

 C. Varley, Balfour Stewart, C. W. (Sir Charles) Siemens, Professor Clerk 

 Maxwell, Dr. Joule, Dr. Esselbach, and Sir Charles Bright, were added to the 

 Committee. 



