480 SCIENTIFIC RECORD FOR 1884. 



legal obm is the resistauce of a column of mercury of a square millime 

 ter in cross-section and 106*=™ in length, at the temperature of uult- 

 ing ice. (2) The conferimce expresses the wish that the French Govern- 

 ment should transmit this resolution to the different states, and recom- 

 mend an international adoption of it. (3) The conference recommends 

 the construction of primary standards in mercury conformable to th^i 

 resolution previously adopted, and the concurrent employment of scales 

 of secondary resistances in solid alloys, which shall be frequently com 

 pared amongst one another and with the primary standard. (4) The 

 ampere is the current the absolute value of which is 10 to the power 

 minus 1 in electro-magnetic units. (5) The volt is the electro-motive 

 force which maintains a current of 1 ampere in a conductor the resist- 

 ance of which is 1 legal ohm. Second section, earth currents and 

 atmospheric electricity : (1) It is to be desired that the results of ob- 

 servations collected by the various administrations be sent each year 

 to the International Bureau of Telegraph Administration, at Berne, 

 which will make a digest of them and communicate it to the various 

 Governments. (2) The conference expresses the wish that observations 

 of earth currents be pursued in all countries. Third section, standard of 

 light: (1) The unit of each kind of simple light is the quantity of 

 light of the same kind emitted in a normal direction by a square centi- 

 meter of surface of molten platinum at the temperature of solidification. 

 The practical unit of white light is the quantity of white light emitted 

 normally by the same source. {Nature, May, 1884, xxx, 20; J. Phys., 

 June, 1884, II, iii, 229.) 



Eowland has completed his determination of the length of the mer- 

 cury column 1 sq. mm. in cross-section which has a resistance of 1 

 ohm. The experiments were made at Clifton, 2 miles from Balti- 

 more, the expense being defrayed by the Government. The resist- 

 ance of columns of pure mercury, contained in glass tubes of various 

 calibers and lengths, was first determined in B. A. units, and then the 

 determination in ohms of the B. A. standard completed the measure- 

 ment. Three methods were used in the latter comparison. The first 

 consisted in heating some non-conducting liquid, such as alcohol or tur- 

 pentine, by the current, in a conductor whose ends were kept at a known 

 difference of potential, the same heating being then i>roduced mechan- 

 ically, thus determining the resistance of the conductor in terms of the 

 work-equivalent of the heat. The secoiid method used was that of 

 Kirchhoff, as modified by Rowland in his 1870 determination of the ohm. 

 The third method was the earth-inductor method of Weber. Unfortu- 

 nately the experiments were not completed in season to have the results 

 communicated to the Paris conference in Ajjril, but they were commu- 

 nicated to the American Electrical Conference held in September in 

 Philadelphia. Rowland gives as the length of the mercury column, as 

 the mean of his experiments, 100.27"". {Science, January, 1884, iii, 10; 

 Elec. World, September, 1884, iv, 101.) 



