568 



SCIENCE 



[N. S. Vol. XXXVI. No. 930 



number of the present N^'a who will live to 

 enter their third year. The other terms of the 

 numerator of formula (A) may be modified 

 in similar manner, giving the formula 



Bi 



Bi 



-Bi 



L= ^ ^ ^" , (D) 



which is applicable to all populations for 

 which we have the following data : the num- 

 ber of individuals born each year since and in- 

 cluding the year in which the oldest individ- 

 uals now living were born, and the number of 

 people of various ages now living. 



While formula (D) has very wide' applica- 

 bility, its usefulness is greatly limited by the 

 fact that it requires so large an amount of 

 data which is usually difficult to obtain. 



Before applying any of these formulae it is 

 necessary to eliminate the effect of immigra- 

 tion and emigration. This means that only 

 those individuals should be considered whose 

 whole life is to be spent as a part of the popu- 

 lation under consideration. In using any of 

 the methods here presented in determining the 

 average rate of depreciation of, say, a farm 

 implement of a given kind, only those imple- 

 ments are to be counted that were bought new 

 (not second hand) and which will presumably 

 be replaced when destroyed or worn out by 

 new ones. W. J. Spillman 



Washington, D. C. 



QUABTEB CENTENNIAL OF TBE IOWA 

 ACADEMY OF SCIENCE 



On Friday and Saturday, April 26-27, the 

 Iowa Academy of Science celebrated the twenty- 

 fifth anniversary of its organization. The ses- 

 sions were held in the Art Gallery of the State 

 Historical Building in Des Moines, beginning at 

 1:30 Friday afternoon. The president's address 

 was given by Professor Louis Begeman, of the 

 State Teachers College, on ' ' The Mission and 

 Spirit of the Pure Scientist." After the presi- 

 dent's address the reading of the usual scientific 

 papers as presented before the academy was the 

 order of the afternoon. As forty-six titles were 

 presented, it was necessary that the time allotted 

 to each paper be very brief. 



The anniversary banquet was held Friday eve- 

 ning at the Chamberlain Hotel, with an attend- 



ance of seventy. At the close of the banquet 

 short addresses of congratulation were given by 

 representatives of neighboring scientific societies. 

 The Nebraska Academy of Science was repre- 

 sented by Professor Addison E. Sheldon, the Illi- 

 nois Academy of Science by Professor Henry B. 

 Ward, the Davenport Academy by Professor G. C. 

 Nutting, the St. Louis Academy by Professor L. 

 H. Pammel, the American Microscopical Society 

 by Professors H. E. Summers and L. S. Eoss and 

 the Ohio Academy by Professor Herbert Osborn. 

 An address on the ' ' Charter Members ' ' was given 

 by Professor L. H. Pammel and the anniversary 

 address by Professor Herbert Osborn, of the State 

 University of Ohio, the first president of the Iowa 

 Academy. 



In accordance with the purpose of the anniver- 

 sary meeting, the session Saturday forenoon was 

 devoted to addresses on ' ' The Development of 

 the Sciences in Iowa during the Past Twenty-five 

 Years ' ' : 



Botany — Professor Thomas H. Macbride. 



Chemistry — Professor W. S. Hendrixson. 



Geology — Professor M. F. Arey. 



Physics — Professor Frank F. Almy. 



Zoology — Professor C. C. Nutting. 

 These papers gave valuable reviews of the 

 status of the sciences in the colleges at the time 

 of the organization of the academy, and historical 

 sketches indicating marked advance in all scien- 

 tific lines during the quarter century. 



At the business meeting, over eighty applica- 

 tions for membership were presented. The meet- 

 ing was in every way fitting to celebrate the end 

 of a quarter century of earnest and effective 

 work done by the academy. 



The 1913 meeting will be held at the Iowa State 

 College, Ames. 



TITLES of papers PEBSENTEI> 



(Abstracts furnished by authors) 

 Ferns and Liverworts of Grinnell and Vicinity: 



H. S. Conard. 

 Secotium warnei, a Stalked Puffiall: H. S. 



Conard. 

 Sirnblnm rubescens in Iowa: H. S. Conard. 

 Aroid Notes: James Ellis Gow. 



In studying the morphology of some twenty 

 species of Aroids, mostly tropical, the writer 

 found that there is great confusion in the nomen- 

 clature of the species. A reference to the original 

 sources has made it possible to give a correct ac- 

 count of the taxonomy of all but one species, and 

 the results are here presented. 



