248 THE PRINCIPLES OF SCIENCE. 



in advance of fact, and assume that all substances are 

 capable of these three forms. Such a generalization was 

 accepted by men of the high intellect of Lavoisier 6 and 

 Laplace f before many of the corroborative facts now in our 

 possession were known. The reduction of a single comet 

 beneath the sway of gravity was at once considered suffi- 

 cient indication that all comets must obey the same power. 

 Few persons doubted that the same great law extended 

 over the whole heavens ; certainly the fact that a few 

 stars out of many millions make manifest the action of 

 gravity, is now held to be sufficient evidence to establish 

 the general extension of the laws of Newton over the 

 sphere of the visible universe. 



Value of Generalization. 



It might seem that if we know particular facts, there 

 can be little use in connecting them together by a general 

 law. The particulars must be more full of useful informa- 

 tion than an abstract general statement. If we know, for 

 instance, the properties of an ellipse, a circle, a parabola, 

 and hyperbola, what is the use of learning all these pro- 

 perties over again in the general theory of curves of the 

 second degree I If we understand the phenomena of sound 

 and light and water-waves separately, what is the need of 

 erecting a general theory of waves, which, after all, is in- 

 applicable to practice until resolved into particular cases 

 again 1 But, in reality, we never do obtain an adequate 

 knowledge of particulars until we regard them as cases of 

 the general. Not only is there a singular delight in dis- 

 covering the many in the one, and the one in the many, 

 but there is a constant interchange of light and knowledge. 



e ' Chemistry/ translated by Kerr, 3rd edit. pp. 63, 77. 

 f 'System of the World,' ditto vol. i. p. 202. 



