INTRODUCTOEY REMARKS. 23 



diametrically opposite the other, it would be said, here you 

 have compensation, a balance, no change in the centre of 

 gravity of the earth ; but we have increased the mean diame- 

 ter of the earth, and a perturbation of our planet, and of all 

 other celestial bodies necessarily ensues. 



The force may be said to be in abeyance with reference 

 to the effect it would have produced, if not arrested, or 

 placed in a state of tension ; but in the act of imposing this 

 state, the relations of equilibrium with other bodies have 

 been changed, and these move in their turn, so that motion 

 of the same amount would seem to be ever affecting matter 

 conceived in its totality. 



Press the hands violently together ; the first notion may 

 be that this is power locked up, and that no change ensues. 

 Not so ; the blood courses more quickly, respiration is accele- 

 rated, changes which we may not be able to trace, take place 

 in the muscles and nerves, transpiration is increased ; we 

 have given off force in various ways, and must, if the effort 

 be prolonged, replenish our sources of power, by fresh chemi- 

 cal action in the stomach. 



In books which treat of statics and dynamics, it is com- 

 mon and perhaps necessary to isolate the subjects of consid- 

 eration ; to suppose, for instance, two bodies gravitating, and 

 to ignore the rest of the universe. But no such isolation ex- 

 ists in reality, nor could we predict the result if it did exist. 

 Would two bodies gravitate towards each other in empty 

 space, if space can be empty? the notion that they would is 

 founded on the theory of attraction, which Newton himself 

 repudiated, further than as a convenient means of regard- 

 ing the subject. For purposes of instruction or argument it 

 may be convenient to assume isolated matter : many con- 

 clusions so arrived at may be true, but many will be 

 erroneous. 



If, in producing effects of tension or of static force, the 

 effort made pervades the universe, it may be said, when the 



