83 
ject of the most enormous extent. If this be so, nature is 
most unlike herself in her greatest extent, and in her most 
wonderful operation. But let us assume the existence of 
such a subject. If it be of the simplest kind, as it must be, 
then it can only be affected in one way, and lie utterly be- 
yond the recognition of mere sense. The one way in which I 
assume this universal subject or medium to be affected is the 
way in which it receives and reacts on the internal conatus 
of all the members of the solar system. This exterior cona- 
tus will be at its maximum of receptivity and reaction in 
the periphery of each orb, and at its minimum in the 
boundary of the solar system. The conatus for density and 
individuality reaches its greatest force in the same periphery ; 
therefore it will happen that the highest result of this action 
and reaction will take place. And this highest result is 
what I call gravitation, which attains its maximum at the 
periphery of the heavenly bodies. But I also assume that 
this assumed universal medium has a conatus of its own, 
independent of the produced conatus for gravitation, and 
that it is a uniform, constant, all-pervading and never- 
failing effort of persistence and resistance which no other, 
excepting the conatus of the sun and planets, can affect. 
Hence every other conatus must bow to its force and obey 
its law. And I take this to be the reason why the law of 
the squares of distance is found to prevail in the forces of 
the air and of luminiferous ether, as well as in every part of 
the solar system. That is to say, the resistance of this as- 
sumed medium is equal to the squares of the distance of the 
sun and planets acting upon it, and its disturbance is the 
disturbance of gravitation. 
In consequence of the constant and universal persistence 
of this assumed conatus and its medium force of a different 
kind, that is, the force which produces motion, can act uni- 
formly throughout it according to its own conatus, just as our 
own bodies can move about in the pressure of atmospheric 
