INTERNATIONAL SCIENCE, 499 



entered into by the ditferent countries at a diplomatic conference 

 lield at Paris in March and April, 1875, means were created for 

 carrying- out the work of verifying- standards under a new inter- 

 national metric committee, and for the purpose of enabling the com- 

 mittee to execute their duties effectually, as well as of securing the 

 future custody and preservation of new metric prototypes and instru- 

 ments, the Permanent Metric Bureau Avas founded. The original 

 cost of the bureau was £20,000, and the annual budget was fixed at 

 £3,000 for the period during which the prototypes were being pre- 

 ])ared, after which time it was expected that the expenditure could 

 1)6 reduced to £2,000. In 1901, however, it reached £4,000, the maxi- 

 mum 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 £1,787 was 

 made as entrance fee, and the annual contribution 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 carried out at Sevres is not confined to the reproduction 

 of metric standards, but measurements of precision in various direc- 

 tions have been made with conspicuous success. Scientific thermom- 

 etry 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 Avhich the length of the meter 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. Guillaiime examined the physical prop- 

 erties of alloys, notably those of nickel steel, and proved the possi- 

 bilit}^ of manufacturing a material which shows no sensible expan- 

 sion 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 con- 

 ference 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." 



a The original committee was appointed in 1861 and consisted of Profs. A. 

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

 Matthiessen. and Mr. F. Jenkins. In the following year Messrs. C. Varley, 

 Balfour Stewart, C. W. (Sir Charles) Siemens, Prof. Clerk Maxwell, Doctor 

 Joule, Doctor Esselbach, and Sir Charles Bright were added to the committee. 



