WAVE OF HIGH WATER. 313 



not essential to the solution of that problem that either the 

 exact nature of the causal force, or the mode of its trans- 

 mission, should be determined. In the science of me- 

 chanics, a single force acting along a given line may be 

 replaced by any two or more forces acting in different 

 directions, whose resultant on that line is equivalent to 

 the single force. The introduction of the idea of rota- 

 tion into the constitution of the ultimate atoms of matter, 

 and the consequent polar character of the action of ag- 

 gregated rotating spheres upon each other, would there- 

 fore merely result, so far as physical astronomy is con- 

 cerned, in replacing an assumed simple force of attraction 

 by combined repulsive and attractive forces, whose re- 

 sultant on the given line would be the exact equivalent of 

 the more simple force. 



But whilst the precise nature of the causal forces may 

 be comparatively unimportant in problems of pure cos- 

 mical motion, the hypothesis of a simple attractive force 

 (an hypothesis which Newton declined to indorse, though 

 adopting its phraseology in his writings) has long been an 

 insuperable barrier in the way of correlating the force of 

 gravitation with the other natural powers. 



In an age when the doctrine of correlation is making 

 rapid advances in the estimation of philosophers, this 

 anomaly cannot much longer be allowed to cast reproach 

 on our fundamental ideas of force, and some such basis for 

 differentiating cosmical and terrestrial conditions of matter 

 and force as that which is offered by the hypothesis of 

 the polarity of all matter is obviously one of the first and 

 most important steps towards demonstrating the unity of 

 the physical sciences. Recurring, therefore, to the mode of 

 the transmission of cosmical force, there is nothing incon- 

 sistent with the Newtonian theory of gravitation in the 

 suggestion already made, that when, in condensing upon a 

 centre, part of the diffused matter from which the solar 



