Record. xliii 



North American woods in tlie American Museum of Natural History 

 in New York. The name Lettennani commemorates his numerous dis- 

 coveries in these little known regions. 



October 20, 1913. 



President Engler in the chair; attendance 46. 

 The following donations to the Museum and Library 

 were reported: 



A. F. Onderdenk. .Fifteen volumes of the Scientific American Supple- 

 ment. 



Gr. R. Agassiz Letters and Recollections of Alexander Agassiz with 



a sketch of his life and work. 



Professor F. E. Nipher addressed the Academy on 

 ''Variations in the Earth's Magnetic Field." 



Dr. H. M. Whelpley gave an illustrated lecture on 

 "Problems in America Archaeology. ". 



The death of Mr. Adolphus Busch, of Mr. Moses 

 Craig, of Mr. Clias. H. Huttig, of Mr. Elias Michael, and 

 of Dr. William Taussig was announced. 



November 3, 1913. 



President Engler in the chair; attendance 26. 

 Professor J. L. Van Ornum addressed the Academy 

 on "Forests and Floods." 



Professor Van Ornum outlined the complexity of the relation between 

 rainfall and runoff. He then indicated that, while exceptions occur 

 and greater differences exist, the general tendency of forests is to 

 somewhat equalize and increase the rainfall locally, to reduce evapora- 

 tion from the soil, to prolong the melting of snow, to retard surface 

 flow and to prevent the erosion of soil in hilly and mountainous coun- 

 try. Yet the essential question is whether this tendency is potent 

 enough to be important. The impossibility was shown of deductively 

 determining the quantitative value of the forest influence, with any 

 approach to satisfactory results, by attempting the evaluation of the 

 different factors contributing to that influence. 



Then four investigations were reviewed, in three of which no ap- 

 preciable effect of extensive change in forest cover could be detected 

 in the runoff phenomena, and in one of them the effect was apparent. 



The conclusion was reached that the forest influence is sometimes 

 considerable on watersheds of small area, but that it is slight on those 

 of moderate extent and generally is entirely imperceptible in its effect 

 on flood flow in the main rivers of large drainage basins. 



