1 84 SCIENCE PROGRESS 



of a body is a function only of its mass and position. Com- 

 paratively recent experiment has suggested that temperature 

 affects slightly the gravitational force produced. V. Cremieu 

 (Comptes Rendus, 165, 586-9, 670-72, 191 7) uses the pendulum 

 method to investigate experimentally whether the gravitation 

 between two bodies is affected by (1) motion of one of the 

 bodies or (2) the presence of lines of gravitational force due 

 to a rapidly moving third body. In each case the result 

 obtained was negative, the order of accuracy being 1 per cent. 

 C. E. Weatherburn (Proc. Camb. Phil. Soc. 19, 72-85, 



191 7) considers Lamia's and Laue's equations of motion of 

 hydrodynamics from the standpoint of relativity, obtaining the 

 analogues of some well-known theorems in ordinary hydro- 

 dynamics. 



The other direction in which much work is now being done 

 is in the dynamics of and through media. This is an immediate 

 effect of the development of the art of flying. In order to achieve 

 success in aeronautics two problems referring to our subject need 

 investigation — motion through a resisting medium and meteoro- 

 logy. The war has reacted profoundly upon this phase of 

 research. Whereas only a few years ago orthodox mathe- 

 maticians stood more or less aloof from aeronautical mathe- 

 matics, the case is quite different now. The successful vindica- 

 tion of the researches of Lanchester and Bryan as leading to 

 criteria of stability and controllability of an aeroplane based 

 on exact mathematical formulation, and the imperative neces- 

 sity to apply the best brains of the country to the solution of 

 the urgent problems of aircraft attack and anti-aircraft defence, 

 have swept away the remains of old prejudice. It is obvious, 

 of course, that much of the work that has been and is being 

 done during the war must remain unpublished, and there can 

 be no doubt that the cessation of hostilities will be followed by 

 the release of an amount of accumulated knowledge and results 

 that will colour the teaching and development of dynamics 

 for many years. Nevertheless, a considerable amount of 

 important work, that has no immediate bearing upon practical 

 military problems, is being published. Among the recent 

 researches that have come to the notice of the writer are the 

 following : 



P. Appell (Comptes Rendus, 165, 694-5, 1917 ; 166, 22-3, 



191 8) discusses the results of experiments made by Z. Carriers 



