PIIEFACE. vii 



way students would be forced to recognise the logical 

 connexion between the different parts of the science. 

 Practically, however, I believe that such a mode of 

 teaching generally leads, at least in the case of begin- 

 ners, to an aggravation of the evils it is intended to 

 obviate. No doubt students who have acquired a little 

 familiarity with geometrical reasoning easily recognise 

 the logical sequence of the propositions, but very 

 often they learn no physics ; the whole matter is for 

 them a rather uninteresting series of exercises on 

 the geometrical principles they already know ; while 

 those to whom the geometry is a difficulty seldom get 

 any benefit at all, either in the way of geometry or of 

 physics. I am convinced that the true way to make 

 the somewhat abstract notions necessarily encountered 

 at the outset of the study of physics intelligible to 

 beginners, is not to emphasise the abstractions, but to 

 provide the learner with the clearest possible ideas of 

 the concrete facts from which the abstractions are 

 derived. In any sound system of teaching, particulars 

 must come before generalities ; for, unless a student 

 has clear conceptions of individual phenomena, it is 

 impossible for him to understand their mutual relations 

 or the general conclusions that are based upon them. 

 But although, in the abstract, the truth of these state- 

 ments is not disputed by anyone, it is not always re- 

 cognised as fully as it should be in the practical teach- 

 ing of elementary physics. It is so obvious that the 

 educational value of this subject depends essentially 



