November 20, 1903.] 



SCIENCE. 



657 



plied to steadily sweeping substances 

 Thus Boltzmann's H function, which has 

 a minimum value and closely corresponds 

 to entropy when a gas is in thermal equilib- 

 rium, has a definite value for any steady 

 state of a gas other than thermal equilib- 

 rium. 



Entropy always increases in natural 

 phenomena, and the notion of entropy is. 

 perhaps, much more intimately related to 

 the notion of time than any other phys- 

 ical notion whatever. The notion of 

 entropy seems to me, indeed, to be the very 

 foundation of the notion of time as a phys- 

 ical fact, although the numerical evalua- 

 tion of time depends, in practice, upon the 

 approximate realization of some of the pre- 

 cise ideas of mechanics. 



This intimate relationship of the notions 

 of entropy and time gives very great em- 

 phasis to the two propositions A and B 

 in article 7 in which increase of entropy 

 appears as measured by elapsed time. 



Heretofore the idea of the increase of 

 entropy associated with a sweeping process 

 has been thought by the ablest writers on 

 thermodj-namics, such as Willard Gibbs, to 

 be dependent upon the devising of a revers- 

 ible process which leads to the same change 

 of state as the given irreversible process. 

 This is, I think, true in regard to sweeping 

 processes in general, but it is not true in 

 regard to steady sweeps. 



The characteristic features of irrevers- 

 ible processes are, in my opinion, very 

 clearly suggested by the tenn sweep and 

 by the special terms simple sweep, trailing 

 sweep and steady sweep, and I urge the 

 adoption of these terms. 



W. S. Franklin. 



Lehigh University. 



METEOROLOGY AT THE BRITISH 

 ASSOCIATION. 



CoNTR.\RY to custom. meteoFologv took 

 foreriiost place at the Southport meeting 



of the British Association. This was 

 largely due to the efforts of Dr. W. N. 

 Shaw, the head of the British Jleteorolog- 

 ieal Office, by whose invitation the Inter- 

 national ^Meteorological Conmiittee met 

 with the British Association for the Ad- 

 vancement of Science and for the first time 

 in England since 1876. The attendance 

 of a ma.iority of the members of the com- 

 mittee justified the innovation, and before 

 going to Southport they were able to meet 

 some representative British men of sci- 

 ence at a dinner in London given by Dr. 

 Shaw. Of the seventeen members consti- 

 tuting the International ]Meteorological 

 Committee, the following ten were present 

 at Southport: the president. Professor 

 Mascart, of Paris ; the secretary, Professor 

 Hildebrandsson, of Upsala; Dr. Shaw, of 

 London ; Dr. Paulsen, of Copenhagen ; Pro- 

 fessor Mohn, of Christiania; Dr. Snellen, 

 of Utrecht: General Rykatcheft', of St. 

 Petersburg; Professor Pernter, of Vienna; 

 Professor Hellmann, of Berlin; and Pro- 

 fessor Moore of Washington. Although 

 the United States has had a representative 

 in the committee for twelve years, only now, 

 for the first time, was a meeting attended 

 by the chief of the "Weather Bureau, indi- 

 cating the present desire of this country 

 to cooperate in international meteorology. 

 Besides the above, there came for the dis- 

 cussion of meteorological telegraphy. Pro- 

 fessor van Bebber from Hamburg and Cap- 

 tain Chaves from the Azores; and of the 

 sub-committee for scientific aeronautics its 

 chairman, Professor Hergesell from Stras- 

 burg, M. Teisserenc de Bort from Paris, 

 and the writer. The sessions of the com- 

 mittee lasted five days and the questions 

 considered related principally to details 

 of administration, publication and obser- 

 vation. Of greater scientific interest was 

 an apparatus, shown by Dr. Paulsen, for 

 the collection of atmospheric electricity by 

 the employment of radioactive salts, and a 



