Notices respecting New Boohs. 489 



usefulness of his final conclusions, we must at least allow that he 

 has put together his own ideas, along with what is best in those of 

 other people (showing with great acuteness what parts of their 

 work are defective), and has arrived at a statement of the matter 

 which may probably not be materially improved for some time to 

 come. 



It is well that we should occasionally find a man obviously 

 capable of higher work, ready to devote himself to the improvement 

 of our views of elementary matters. Things like this have but 

 little influence on the advance of science. Every man who is really 

 scientific knows them well enough to avoid mistakes of application ; 

 still it is useful to have our attention called to the slips which even 

 the greatest physicists are liable to make in the language they 

 employ when dealing with matters which appear to them all but 

 self-evident. 



Most of the faulty passages detected by the author appear to owe 

 their origin to some form or other of the pernicious doctrine called 

 the Principle of Sufficient Reason, a piece of metaphysics which has 

 choked off from true science many a man who might have done it 

 genuine service. When an uncogged die is thrown there is no 

 reason, to our knowledge, why it should give 1, rather than 2, or 

 any other number of points up to 6. This all will allow. But 

 would any one think of arguing from it that the die should, when 

 thrown, stand on one corner so as to avoid preference where all 

 choices are equally likely ? The analogy is rather overdrawn, but 

 it is quite near enough to show the essential fallacy of the so-called 

 doctrine or principle. 



As to "Force," the question of its non -objectivity has been 

 briskly discussed in this country of late years ; and Dr. Streintz's 

 remarks on this part of the subject seem to accord, at least fairly, 

 with those newer views in which what is commonly called force is 

 looked upon as a mere indication of sense which, like sound or light, 

 is something totally different from the objective reality. Put in a 

 word or two, his point of view is that a body's motion undergoes 

 acceleration to an amount, and in a direction, depending on the con- 

 figuration of the system of which it forms a part. But we cannot 

 help expressing the conviction that the author would have much 

 strengthened his case, had he at once accepted (as a result of ex- 

 periment) the Conservation of Energy in its full extent. Till that 

 is done, it seems to us that one of the most important factors of 

 our final determination is left entirely out of court. 



We conclude by recommending the work to the careful and 

 serious attention of all who have to deal with the physical bases of 

 our whole scientific knowledge, which are, and must ever be, the 

 only genuine ones. 



