554 



SCIENCE. 



[N. S. Vol. XL No. 275. 



basins. This mode of explanation of the tides, 

 •which has not yet been published, asserts that 

 " In most cases the dominant ocean tides have 

 their origin in definite systems whose free 

 periods of oscillation are very nearly those of 

 the tidal forces ; and that the time of high or 

 low water in each is the time when the virtual 

 work of the tidal forces upon the system be- 

 comes zero." The time and height of the tides 

 in Lake Superior and the eastern portion of 

 the Mediterranean Sea, as computed by the cor- 

 rected equilibrium theory, were found to agree 

 with observations quite well. A number of lo- 

 calities forming fractional areas having de- 

 pendent stationary waves were enumerated, the 

 tides in the Gulf of Suez and in the Gulf of 

 Maine being selected as examjiles which were 

 somewhat fully explained. 



Mr. L. A. Bauer then exhibited a number of 

 lantern slides showing photographs of distin- 

 guished men in the line of Meteorology and 

 Magnetism. A number of views of noted mag- 

 netic observatories were also given. On account 

 of the lateness of the hour Mr. Bauer was 

 obliged to omit a descriptive paper which he 

 had prepared on the subject. 



E. D. Preston, 



Secretary. 



DISCUSSION AND COBBESPONDENCE. 



BLBCTKICAL UNITS AND THE INTERNATIONAL 

 CONGRESS. 



In Mr. Wolff's interesting article on the 

 ' Electrical Standards of the Office of Weights 

 and Measures (Science, March 16, 1900), there 

 is an unjustifiable criticism (unintentionally so, 

 I have no doubt) of the work of the Interna. 

 tional Congress of 1893, in defining the three 

 fundamental units. 



A careful reading of the official report of the 

 Chamber of Delegates will show that a special 

 effort was made to avoid the error which Mr. 

 Wolfi" thinks the Congress committed. As the 

 official Proceedings include little of the dis- 

 cussion which occurred during sessions lasting 

 nearly a week, a brief reference to the history 

 of these definitions may be useful. A large 

 part of one of the early sessions was spent in 



discussion, which almost became controversy, 

 of the definitions of the ohm, ampere and volt. 

 A set of definitions was submitted by the 

 American delegates which were primarily rigor- 

 ous, essentially those of the British Association 

 Committee, the material representations being 

 defined as approximations. The idea was to 

 adopt definitions which in themselves would 

 never need revision, leaving the way open, 

 however, to any better approximations in ma- 

 terial standards that might be possible in the 

 future. These definitions were advocated by 

 the American and English delegates, but they 

 were opposed by the German and French mem- 

 bers of the Chamber. At the end of the day it 

 looked as if the Chamber might not be able to 

 come to an agreement upon even the funda- 

 mental units, and to avoid so unfortunate an 

 issue a Committee consisting of Blessrs. Von 

 Helmholtz, Mascart, Ayrton and Mendenhall, 

 with the President of the Chamber, Professor 

 Rowland, was appointed to bring In a report 

 defining the ohm, ampere and volt at the next 

 session. 



This committee reported on Thursday, Au- 

 gust 24th, and its conclusions, which were 

 unanimously adopted by the Chamber, became 

 the basis of all subsequent work. 



It will thus appear that the definitions of the 

 fundamental units as issued by the Interna- 

 tional Congress were not exactly what the 

 American and English delegates would have 

 chosen, but some sort of a compromise was 

 necessary in order to avoid a failure. Care was 

 taken, however, to see that there was really 

 no inconsistency or absurdity present or possi- 

 ble in the language used. The ampere is said 

 to be ' represented sufficiently well for practical 

 use by, etc.,' and in the definition of the volt the 

 same phrase occurs so that the ampere is not 

 declared to be a current of a certain silver de- 

 positing power, nor is the volt declared to be 

 a certain fraction of the E. M. F., of a Clark 

 cell. A variation of the same language is used 

 in defining ohm but it was found impossible to 

 get exactly the same words in. When, in 1894, 

 Congress enacted a law legalizing these units, a 

 few slight verbal changes were made without 

 altering the meaning. 



T. C. M. 



