330 Mr Carpenter on the Differences of the Laws 



will be found useful for practical purposes, and will be fre- 

 quently referred to in subsequent observations. 



6. The manifestation of the properties of matter, in the ac- 

 tions which bodies, placed in certain relations to one another, 

 present to our observation, gives rise to our idea of power. 

 Thus, when two bodies possessed of the property of gravitation 

 are placed within the sphere of each other's attraction, the power 

 of gravity is developed, and manifested by their approach to 

 one another. Or when a piece of iron is brought near a magnet, 

 the electric equilibrium of the former is disturbed, and the at- 

 traction caused by the opposite electric state of the neighbouring 

 parts of the two bodies gives rise to their tendency to approxi- 

 mate ; or in common language, the magnetic power causes their 

 motion towards each other. Of the abstract nature of any 

 power, as of matter itself, we know nothing ; it is only recog- 

 nisable by its effects ; but it is, as we have seen, to be ulti- 

 mately referred to the properties of matter, which may be re- 

 garded as axioms or postulates on any course of reasoning 

 founded upon them. Of power as a cause of effects, it is gene- 

 rally acknowledged that we judge of it only by its invariable 

 connection with subsequent phenomena. 



7. To the term principle no very definite meaning can be at- 

 tached. It has been remarked that " this word, characteristic 

 of a less advanced state of science, has been generally employed 

 (as the final letters of the alphabet are used by algebraists) to 

 denote an unknown element, which, when thus expressed, is 

 more conveniently analysed.''* Thus we speak of the principle 

 of electricity, or of the principle of magnetism, as the unknown 

 causes of certain phenomena that are as yet imperfectly under- 

 stood. When the laws of these phenomena, however, are per- 

 fectly ascertained, they terminate in referring all of them to 

 simple properties of matter, from which they may be deduced 

 by demonstrative reasoning, just as all geometrical theorems 

 are founded on the axioms first assumed. It has been in the 

 science of life that the term Principle has been most used, and 

 most abused ; the conditions of vital phenomena are not yet de- 

 termined with sufficient precision to enable us to refer all ob- 



" Mayo's Physiology, p. 2. 



