EEVIEWS — ANALYTICAL STATICS. 65 



conque." This Mr. Todhunter has rendered " Matter is every thing 

 that affects our senses." If we must have a definition of matter, 

 surely it is worth while to make the wording as little liable to objec- 

 tion as may be ; and Poisson' s own words evidently shut out one 

 verbal objection to which Mr. Todhunter's is liable, though it is only 

 fair to remark that this imperfection is common to Mr, Pratt's ver- 

 sion. Both the English writers, following Poisson, proceed to define 

 "a body" as " a portion of matter limited in every direction, and 

 consequently of definite form and volume" ; the mass of a body as 

 " the quantity of matter which it contains"; and a material particle 

 as "a portion of matter indefinitely small in every direction." This is 

 the substance of the first sentence in Mr. Todhunter's book, and we 

 would ask in what respect the student is made wiser by reading 

 these dry dogmatic definitions. And above all, why should such a 

 form be adopted in 1853 for the commencement of a treatise on 

 Statics ? We have advanced a good deal in freedom of using analy- 

 tical methods since Poisson wrote his treatise. Then the method of 

 formal statement of definitions (derived apparently from the synthe- 

 tical systems of the older geometry) was still in repute — and a 

 writer must needs begin his treatise with a string of definitions, be- 

 cause Euclid does so. Hence, as far as we can see, that propensity 

 to over-define which too often characterises English works on mathe- 

 matics. We met with an instance lately which well illustrates this 

 propensity : the author of a treatise on Dynamics published a few 

 years ago at Cambridge, (Professor Wilson) after remorselessly defi- 

 ning almost every thing he can lay his hands on, tells U3 with a half- 

 doubting forbearance, that " It would be useless to attempt to define 

 space and time. No explanation could in any way render the ideas 

 clearer." But in the sentence which immediately follows that which 

 we have quoted, Professor Wilson does point out a distinction which 

 the writers on "Introductions and Definitions" in treatises on Me- 

 chanics generally would do well to bear in mind. After saying that 

 space and time require no definition, he adds, " The measures of 

 them on the contrary require the greatest attention." It is, we con- 

 ceive, because this distinction is attended to that the commencement 

 of the later French treatises on Mechanics — such as those of Poin- 

 sot or Duhamel for instance, — is so much more attractive than the 

 corresponding part of the works of Poisson and his translators. In 

 the former writers we are allowed to have an idea in our own mind 

 concerning the mass of a body, but when we come to the point 

 where it is needed, we are told how mass is to be estimated numeri- 

 cally — we are informed when two bodies are said to have the same 



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