THE 

 LONDON, EDINBURGH, and DUBLIN 



PHILOSOPHICAL MAGAZINE 



AND 



JOURNAL OF SCIENCE. 



[FIFTH SERIES.] 



SEPTEMBER 1893. 



XXIII. On the Hypotheses of Dynamics. By Prof. J. GL 

 MacG-kegor, D.Sc, Dalhousie College, Halifax, N. S* 



PROFESSOR LODGE'S paper on the Foundations of 

 Dynamics f, in which he criticises an Address of mine 

 on the same subject { and replies to criticisms I have made § 

 on a series of papers by him in this Magazine |j, contains so 

 much debatable matter that it would require more space than 

 is available to give it full discussion. There are some points, 

 however, which are of so much importance in the clearing 

 up of our conceptions of the fundamental assumptions of 

 Dynamics, that I venture in as brief a manner as possible 

 to draw attention to them. 



(1) The Relativity of the First and Second Laws of Motion. 



Prof. Lodge completely misunderstands the objection which 

 was urged in my Address against the usual statement of the 

 first and second laws of motion, and which had been pre- 

 viously urged by various writers If. He states it to be " that 



* Communicated by the Author. 



t Phil. Mag. current volume, p. 1. 



X Trans. Roy. Soc. Canada, vol. x. (1892), sec. iii. p. 3. 



§ Phil. Mag. vol. xxxv. (1893) p. 134. 



|| Vols. viii. (1879) p. 277, xi. (1881) pp. 36 & 529, xix. (1885) p. 482. 



51 The list of writers which Prof. Lodge gives is obviously not intended 

 to be complete. It omits C. Neumann ( Ueber die Principien der Galilei- 

 Newtonschen Theorie, Leipzig, 1870), Prof. J. Thomson (Proc. R. S. Edin. 

 vol. xii. pp. 568 & 730), Prof. Tait (ibid. p. 743 and ' Properties of Matter,' 

 1885, p. 92), H. Streintz (Die physikalischen Grundlagen der Meehanik, 



Phil. Mag. S. 5. Vol. 36. No. 220. Sept. 1893. R 



