proceedings: the philosophical society 537 



for the purpose of reducing the loss of water. In view of these changes, 

 wide variations as regards efficiency in use of water by different plants 

 might be expected. The authors found this to be the case. The amount 

 of water transferred is very great compared with the dry matter pro- 

 duced. In the experiments direct evaporation from the soil was pre- 

 vented by the use of perforated covers, the openings about the stems of 

 the plants being sealed with wax. Six pots were used for each variety, 

 to provide a basis for calculating the probable errors of the water require- 

 ment ratios. The water requirement is profoundly modified by differ- 

 ences in climatic environment. The average for 25 varieties grown at 

 Akron, Colorado, in 1912 was only 79±2 per cent of that of the same vari- 

 eties in 1911, while the evaporation in 1912 was 78 ± 2 per cent of that 

 in 1911. Paper was illustrated by photographs and lantern slides. 

 Upon request of the chair, Mr. Shantz made some additional remarks 

 concerning the investigation. Botanists were interested in this question 

 as early as 1699. The paper was discussed by Messrs. Bowie, Curtis, 

 CoBLENTZ, Humphreys, and Wenner. 



Mr. M. D, Hersey then gave a brief review of the Birmingham meeting 

 of the British Association. In the Engineering Section great interest was 

 shown in the discussion of complex stress distribution and failures and in 

 report on electrical units and nomenclature. .In the Physical and Mathe- 

 matical Section the papers dealt chiefly with modern theories of radia- 

 tion. Reference was made to the Presidential and Vice-Presidential 

 addresses and the relatively greater importance attached to the social 

 and general features than with the American Association. 



Upon the suggestion of Mr. Hersey, the chair invited Mr. W. F. G. 

 SwANN to give informally brief abstracts of his papers before the Bir- 

 mingham meeting on The electrical resistance of thin metallic films and on 

 The exj)ression for the electrical conductivity of a metal. The first give a 

 theory to explain the abnormally high apparent specific resistance of a 

 very thin film, while the second called attention to the fact that Drude's 

 expression requires a correction in coefficient in denominator from 4 to 3. 

 At 10 p.m. the meeting adjourned. 



The 728th meeting was held on October 25, 1913, at the Cosmos Club, 

 Vice-President Bowie in the chair; 30 persons present. 



Mr. J. H. Bellinger presented a paper on The measurement of high 

 frequency currents. Three effects made use of in such measurements are 

 electro-dynamic, electro-static, and thermal. The last is most success- 

 fully and generally used and four methods involving this effect were dis- 

 cussed. The different appliances, experimental apparatus, and standard 

 instruments were briefly described. The theoretical considerations and 

 formulae were discussed. The conclusions drawn were that circuit of 

 ammeter must be simple, the straight wire type of instrument is superior, 

 and that errors may be eliminated by use of high resistance. The paper 

 was discussed by Messrs. Olshausen and Rosa. 



Mr. F. W. Wells then presented by invitation a paper entitled 



