REVIEWS — ANALYTICAL STATICS. 67 



the hands of a pupil previously ignorant of the suhject : the pupil 

 finds the book commencing with a series of definitions, on which he 

 naturally imagines that the science is to be built. The first of these, 

 and a fair sample of them is, " Matter is whatever affects our senses" 

 — passing over the objection arising from imperfect translation, he 

 comes to his tutor next morning, and asks whether light and electri- 

 city are matter, as they certainly affect our senses. Tutor points out 

 that the definition is rather loosely worded : points out that it might 

 perhaps be made less imperfect by adding the words ' or that through 

 which impressions may be conveyed to our senses': rather doubts 

 whether such an addition will do much good, and finally remarks 

 after all it is scarcely worth while wasting time over it, as the defi- 

 nition is not one of any practical value. Upon which the pupil 

 stares, doubts, and finally asks whether then the definition had not 

 better have been left out ? To which query the reply is necessarily 

 in the affirmative — after which the pupil's faith in the necessity and 

 usefulness of the introductory chapter is probably reduced below 

 zero ; and after a few more examples of the kind it will be very dif- 

 ficult to induce him to pay attention to explanations and distinctions 

 that are really essential. 



We must now say a few words as to the fundamental principles on 

 which the science of statics is made to rest, and the grounds on 

 which they are required to be received. There are, we conceive, 

 two grand principles on which the whole of the science depends, viz. 

 the inertia of matter, and the transmissibility of force. The former 

 principle as applied to Statics is this : " A body once at rest will re- 

 main at rest unless some force is applied to it : and any single force 

 applied to a body at rest will necessarily set it in motion." In other 

 words, matter has no power either to move itself or to prevent force 

 moving it. This principle appears again in Dynamics, as the first law 

 of motion, and the complete statement of the principle will be that 

 u Matter has no power of itself to change its state of rest or mo- 

 tion," remembering that a body's state of motion is changed when 

 either the direction or the rate of its motion is altered. This prin- 

 ciple then is a fundamental one : it is one which lies at the very root 

 of our systems of Mechanics : how are we to establish its truth ? Or 

 can we establish its truth at the outset ? And especially can we so 

 establish it as to trust the proof of it in the hands of a beginner ? 

 These questions M. Poisson, and after him both Messrs. Pratt and 

 Todhunter answer in the affirmative. Poisson's remark, according 

 to Mr. Todhunter's version, is as follows : 



