312 



SCIENCE 



[N. S. Vol. XLIII. No. 1105 



A. 0. True, of Washington, D. C, is the dean 

 of the school, and the assistant dean is Pro- 

 fessor Charles E. Marshall, director of the 

 graduate school and professor of microbiology 

 at the Massachusetts College. The school is 

 open to all college graduates. Its purpose is 

 for the study of the recent development in the 

 natural, social and economic sciences as ap- 

 plied to agriculture, as well as in the technical 

 branches of the so-called practical agriculture. 

 Courses are offered in (1) growth, (2) produc- 

 tion, (3) rural organization, (4) agricultural 

 education, (5) distribution-marketing, (6) 

 land problems, (7) adjunct course in physico- 

 chemico-physiological elements, (8) special lec- 

 tures and conferences. 



From May 1 to November 30, fourth-year 

 medical students at Toronto will be given a 

 summer course to qualify for their degree, and 

 there will be no fifth-year course nest year at 

 the university. The summer session will last 

 twenty-six weeks. There will be sixty men who 

 will attend the summer session, and when they 

 graduate they will be in a position to accept 

 positions with the various hospital units. It 

 is understood that Queen's University, Kings- 

 ton, will take a similar step. 



The trustees of iNrorthwestern University at 

 their last meeting filled the vacancy in the 

 deanship of the dental school, which occurred 

 through the death of Dr. Greene Vardiman 

 Black on August 31 of last year, by the elec- 

 tion of Thomas Lewis Gilmer, M.D., D.D.S., 

 Se.D. 



At Smith College, Dr. Joel E. Goldthwaite 

 has been appointed professor of hygiene and 

 physical education, and Miss Pauline Sperry, 

 assistant professor of mathematics. Miss Har- 

 riet E. Cobb has been promoted to be professor 

 of mathematics; Dr. Mary M. Hopkins to be 

 associate professor of astronomy, and Mrs. 

 Anna B. ifTewell to be assistant professor of 

 zoology. 



At Harvard University Dr. Dunham Jack- 

 son has been promoted to an assistant pro- 

 fessorship of mathematics. 



The chair of botany in the Alabama Poly- 

 technic Institute and Agricultural Experiment 



Station, vacant by the resignation of Dr. 

 J. S. Caldwell to take up the position of " By- 

 products Specialist " for the Washington 

 Agricultural Experiment Station, has been 

 fiUed by the appointment of W. J. Eobbins, 

 Ph.D. (Cornell), instructor in botany in the 

 ISTew York State College of Agriculture. 



DISCUSSION AND CORRESPONDENCE 



THE FUNDAMENTAL EQUATION OF 

 MECHANICS 



Mr. Kent's recent letter on the " Teaching 

 of Elementary Dynamics,"^ with much of 

 which I heartily agree, contains one serious 

 error which I think should not pass unnoticed. 

 As this error seems to me a not unnatural re- 

 sult of one featiwe of his favorite method of 

 beginning the study of mechanics, I should 

 like to take this opportunity to summarize, in 

 a brief review, the three methods of beginning 

 mechanics which have been advocated resi)ec- 

 tively by Mr. Kent, Professor Hoskins and 

 myself.^ To do this, I propose first to state 

 briefly certain dynamical principles on which 

 we all agree; I shall then endeavor to show 

 that precisely these non-disputed facts are all 

 that the student needs to know in order to solve 

 dynamical prohlems, provided he follows my 

 method. It is only when he endeavors to fol- 

 low one of the other methods that he is led 

 into controversial territory. If undisputed 

 facts are suificient for the solution of problems, 

 why burden the student's mind (except as a 

 matter of historical interest) with needless 

 disputations ? 



I. The following statements will, I believe, 

 be accepted as true by all of us, though the 

 emphasis placed on the various items would 

 doubtless vary. 



1. A force is a familiar notion which may 

 be thought of as a push or a pull. Any given 

 force may be identified, that is, preserved for 



1 Science, December 24, 1915. 



2 See articles in Scienoe by L. M. Hoskins, De- 

 cember 4, 1914, April 23, May 7, August 27 and 

 September 10, 1915; by E. V. Huntington, Feb- 

 ruary 5 and July 30, 1915; and by William Kent, 

 March 19 and December 24, 1915. 



