37 



An immense variety of propositions have been made from 

 time to time with the object of establishing something like a 

 definite unit of light, but up to this time with only partial 

 success. The International Congress of electricians, assembled 

 in Paris in May, 1884, adopted the proposal of M. Violle, 

 fixing as the unit the quantity of light emitted by a thread of 

 platinum of a thickness of a square centimetre heated to melting 

 point, and tested at the moment of cooling ; but difficulties 

 occur in this which will effectually prevent it remaining the 

 ultimatum. 



It is a field of inquiry that to many scientists has a great 

 fascination, and is now attracting much attention from 

 specialists. I met persons in London who devoted the greater 

 part of their time to researches in this direction, which will 

 seem, however, to the general public a somewhat restricted 

 specialty. 



Some systems which have been proposed are as follows : — 

 Keat's standard sixteen-candle oil lamp, the French Carcel oil 

 lamp, Crooke's radiometer, the selenium photometer, Lewis 

 Thompson's one-candle standard lamp, &c, &c. 



The British Standards Department, besides carrying on the 

 duties indicated above, give attention to such matters as the 

 following : — Advising all British dependencies as to the best 

 course to pursue in all matters relating to weights and mea- 

 sures ; issuing reports periodically as to the business done 

 under the Act, together with instructions and advice to 

 inspectors as to the best mode of carrying on their duties ; 

 directions for testing all descriptions of weighing-machines ; 

 adjudging limits of errors to be allowed in weights and mea- 

 sures ; inquiring into questions of various metal gauges and 

 screw threads from time to time ; attending international 

 conferences in Paris and elsewhere as to the metric system, 

 unification of longitude, &c. ; testing petroleum-testing appa- 

 ratus ; conducting numerous scientific researches as to expan- 

 sions and contractions of metals and other substances, together 

 with other matters. It will be seen from this list that the 

 scope is very wide and comprehensive. 



CCXN'CLTJSIOIS'. 



I have now described the British Imperial system of stan- 

 dards, which is, so far as it goes, excellent. But theoretically 

 it is far from perfect. Standards of length, weight, capacity 

 (dry, fluid, and gas), and light are alone represented; but an 

 ideal system would represent besides these electric units and 

 meters, atomic units, musical pitch, time, alcohol, temperature, 

 motion and power, &c. 



"With regard to electricity, a unit is now taking form, and 



