Notices respecting New Books. 487 



w for North, South, East, and West respectively; then the 

 resultant transfer of air during the interval since the last 

 reading will be 



kx/ {(n-sy + (e-wy\i; 



and its direction measured from North towards East will be 

 given by the equation 



tan#= . 



LIV. Notices respecting New Boohs. 



Die pliysikalisclien Grundlagen cler Mechanik. Von Dr. Heinrich 



Streintz. Leipzig : Teubner, 1883. 

 TT is not an easy matter to characterize this book ; for, though the 

 -*- author abjures, in the most defiant manner, all aid from the so- 

 called " Erkenntnisstheoric," it cannot be said that he is always quite 

 free from those metaphysical subtleties which loom so large and 

 mean so little. Yet, on the whole, the genuine physicist shines 

 out, though occasionally through the clouds of vain imagination. 

 We will therefore confine our remarks to that part, by far the 

 larger part, of the work which is free from this earth-born con- 

 tamination. 



The author's object is to discuss the fundamental laws of 

 Dynamics — what we are accustomed in this country to call Newton's 

 Laws of Motion. But much more than half of the work is devoted 

 to the First Law, or Galilei's Principle as it is justly entitled. This 

 discussion is extremely interesting, especially from the historical 

 point of view ; for the author has evidently read much, and is not 

 only always a keen, but usually a really discriminating, critic. His 

 citations from the works of C. Neumann, who is w T ell known as an 

 expert mathematician but by no means known as a sound physicist, 

 are to be justified only on the ground that he was a student under 

 that Professor. But his citations from Schell and other authors 

 (or rather, compilers) of little note are quite unnecessary, especially 

 as he has found far higher game in men like Euler, Poisson, Laplace, 

 Lagrange, Kirchhoff, and Clerk-Maxwell. There can be little 

 doubt that he has succeeded in showing that each of these men, 

 some of them on more than one occasion, has been guilty of false 

 logic, or, at least, of inconclusive reasoning in parts of the very 

 elements of Dynamics. Those who are curious to find what these 

 errors are, must be referred to the work itself ; it is sufficient that 

 we indicate that they are to be found there. 



Every one knows the fundamental difficulty which arises when 

 we try to think of absolute, as distinguished from relative, position, 

 velocity, or acceleration. Euler endeavoured to realize the unthink- 

 able, in this case, by a process which virtually amounts to making 



