OF VITAL ACTIONS IN GENERAL. 27 



would fall towards each other (the distance traversed by each being in 

 proportion to the size of the other), and would meet in their common 

 centre of Gravity. Hence it is evident that the attractive force is 

 similar in both bodies ; and our idea of the property of Gravitation must 

 be extended, therefore, from the Earth to the Moon. Again, we find 

 ample reason to believe that the same force acts between the Sun and the 

 Planets, between the Planets and the Sun, and amongst the Planets 

 themselves ; and further, careful experiment shows that masses of matter 

 upon the Earth's surface are not only attracted by it, and attract it in 

 their turn, but that they attract and are attracted by each other. Hence 

 we arrive at the idea of the universality of this property of mutual at- 

 traction ; and we perceive that, in spite of varieties in the actions it 

 produces, and of differences in the amounts of the forces to which it 

 gives rise, the property is the same throughout ; so that we can predict 

 all these actions, and anticipate the forces which will be developed, from 

 the simple general expression of the property of Mutual Attraction, and 

 of the conditions under which it is manifested, constituting the Law 

 of Gravitation or Mutual Attraction. 



20. Now in this case of Mutual Attraction, we have no opportunity 

 of witnessing the dofmant condition of the property in any mass of 

 matter ; for, as nothing is wanting but the presence of another mass to 

 call this property into operation, it is always generating force, and 

 giving rise to actions. If we could conceive of the existence of but a 

 single mass of matter in the universe, we shall at once see that though 

 possessed of the property of mutual attraction, it would not be able to 

 exercise it, so as to generate an attractive force, or to produce a move- 

 ment. 



21. But we will turn to another case ; in which there is a closer 

 analogy to the condition of living beings ; and by which, therefore, the 

 view here put forth may be more clearly illustrated. When a magnet 

 (itself a bar of iron, having no peculiarity of appearance) draws towards 

 it a piece of iron, we say that a Magnetic action or phenomenon takes 

 place ; further, we speak of the power which produced the movement, 

 as the Magnetic force ; and we attribute this force to a certain property 

 inherent in the Magnet, by virtue of which it draws towards itself all 

 pieces of iron that are within the sphere of its operation, and we speak 

 of the iron bar as endowed with the property of Magnetic attraction. 

 Now we cannot ascertain the presence or absence of this property in a 

 certain bar of iron, by any difference in its aspect, its specific gravity, 

 its chemical properties, nor, in fact, by any other mode than the putting 



t in circumstances adapted to call the Magnetic property into action if 

 it really exist : thus we dip it into iron filings, and judge by their ad- 

 hesion whether it is capable of attracting them ; or, as a still more deli- 

 cate test, we ascertain whether it is capable of exerting any repulsive 

 power on a delicately-suspended needle already magnetized. Again, a 

 needle, or bar of iron, which exhibits this magnetic power of attracting 

 other portions of the same metal, exhibits another power, which would 

 seem at first sight totally distinct ; namely, that of constantly turning 

 one of its extremities towards the north, and the other towards the south, 

 when it is so supported as to be free to do so. And yet there is no 



