APPLIED MATHEMATICS i8i 



astronomer, the physicist, and even the philosopher, have 

 derived considerable benefit from the fertile mind and mathe- 

 matical abihty of this most distinguished product of French 

 genius. Acta Math., 38, 192 1, 1-402, consists of an appreciation 

 of Poincare's work, entitled " Henri Poincare, in Memoriam." 

 The applied mathematician will be particularly interested in 

 articles by W. Wien : " Die Bedeutung Henri Poincares fur 

 die Physik " ; by H. A. Lorentz : " Deux memoires de Henri 

 Poincar^ sur la physique mathematique " ; by M. Planck : 

 " Henri Poincare und die Quantentheorie " ; by H. v. Zeipel : 

 " L'oeuvre astronomique d'Henri Poincar^." The last article 

 betrays the extraordinary width of Poincare's interests in 

 dynamical theory and in celestial mechanics, embracing as it 

 did such topics as the tides, figure of the earth, figures of 

 equilibrium of rotating fluids, planetary and lunar theory — 

 with the famous Poincare's theorem on the integrals of the 

 restricted problem of three bodies — besides mathematical 

 methods of great importance in modern dynamical theory, 

 like integral invariants, etc. An interesting feature of this 

 issue of the Acta is an analysis of Poincare's works, written 

 by himself. There is no biography — which is a pity — but 

 an excellent portrait is added to this appreciation of Poincare's 

 labours in the various domains of the exact sciences. Although 

 it was ready in 191 6, the volume could not be issued till last 

 year, owing to difficulties caused by the war. 



Poincar^ was among the earliest to recognise the far- 

 reaching importance of the views contained in Einstein's 

 first papers on relativity. When Einstein was appointed 

 professor at Zurich, Poincard wrote of him as one of the most 

 original thinkers he had ever known : " What we most admire 

 in him is the ease with which he assimilates new conceptions, 

 and deduces from them all their consequences." It is there- 

 fore the more interesting to witness the reception given to 

 Einstein's theories by the French mathematicians and 

 physicists, most of whom, no doubt, were profoundly influenced 

 by the views and methods of their great compatriot. 



French scientists are in fact engaged in exhaustive and 

 critical study of the foundations and consequences of the 

 theory of relativity. Occasionally the criticism is somewhat 

 unscientific in temper, as in the case of M. Gandillot, who 

 commences the preface to the booklet called " lather ou Rela- 

 tivity" (Gauthier Villars, Paris, 1922) in the following manner : 

 " Voltaire, who knew the Germans well as having lived some 

 time in their midst, said that when two Germans converse 

 without understanding one another, then they are talking 

 metaphysics ; but when the conversation reaches such heights 

 that each one does not understand himself, then they are 



