

the Foundations of Dynamics, 7 



but his underground work need not be decorated with fanciful 

 and laborious conceits, it may be as plain as it is substantial, 

 and he may leave its edges rough in order to connection with 

 structures as yet unbuilt and unimagined. 



Of this plain and substantial character would I seek to keep 

 the laws of motion. If a statement like the first law of 

 motion cannot be made in simple and readily intelligible 

 language, I should despair of Physics. In that case the Physics 

 of the future could be little better than a barbarous jargon of 

 technicalities. There are plenty of really difficult places where 

 technical language and unfamiliar modes of thought are 

 for the present essential. The developments of the super- 

 structure erected during the present century are indeed now 

 so stupendous that for myself I should be satisfied if, without 

 appreciably adding to them, I could by consolidation and 

 restatement remove the necessity for some of this artificiality, 

 and so make their harmony and beauty more readily appre- 

 ciated. But in order to do this a simple and unlaborious foun- 

 dation is a necessity. I hope to try before long to display the 

 bold outlines of the foundation already laid by men of sur- 

 passing genius, every unnecessary accretion being cleared 

 away, and the whole simplified to the uttermost ; and then, 

 if the attempt be not too ambitious, I should wish to extend 

 the process to some portion of the superstructure. 



Part II. 



The First and Third Laivs of Motion, 



So much for general preamble ; now turning to Dr. 

 MacGregor's address, we find that he objects to the Newtonian 

 statement of the first law of motion on the same ground that 

 Prof. Karl Pearson, Prof. Mach, Mr. Macaulay of King's 

 College, Cambridge, and several others'* have objected to 

 it, on the ground, namely, that uniform motion is unin- 

 telligible or meaningless unless you specify its direction 

 and velocity with reference to a set of axes. And directly 

 you try to specify axes you get into difficulties, for, although 

 a uniform translation is permissible to them, any rotation 

 or any acceleration of the axes is fatal to a simple state- 

 ment of the behaviour of a body acted on by no force. It 

 is useless to say that the axes must be stationary, because 

 one cannot define what that means ; so the attempt is made 

 to say that the axes must not rotate and must not be acted on 

 by force ; but this last condition is of no use unless they possess 



* See for instance a correspondent in ' Nature/ vol. xxxvi. p. 366. 



