SUN FORCE AND EARTH FORCE. 
329 
pliers than the natures of snn force and earth force. Newton, who 
first gave us clear views of the fact that there is a force resident 
in matter, that is in the earth, as well as in the snn — for the sun 
force was recognized from the earliest of days, — designates earth 
force as the vis insit a, or in other terms the vis inertias. Of the 
character of this force of inertia he gave no explanation, but 
left it rather to be inferred that he was treating of an ultimate 
property of matter to be accepted as final and unexplainable. 
In course of time, Newton himself changed his original 
views. He gave up the hypothesis of the vacuum of space 
to which at one time he fondly clung : he gave up the hypo- 
thesis of a primitive impulse, and he based, in his later days, 
all his explanations on the theory of a universal ether or 
medium through which matter was suspended, which formed 
as it were a solution of matter, and which, by its presence in 
greater or lesser quantity, if such a term be allowable, deter- 
mined the structure of all bodies. This ether was capable, he 
thought, of contraction and of dilatation, and the particles of 
every substantial thing were separated from each other by it, 
and were set into motion through its changes or modifications. 
Attempts have been made to demonstrate that sun force 
and earth force are the same, and that in using two terms we 
are only recording first impressions of natural phenomena ; 
describing in words of a simple kind that which seems to be 
rather than that which is. Lord Bacon would appear to have 
had some such thought as this in view, when he gave utterance 
to the singularly beautiful sentence that “ heat and cold are 
the two hands of nature.” But the philosopher who first boldly 
asserted the unity of the two forces was a man much less 
known, though certainly not less learned than the great Lord 
Chancellor. I mean a man of our own time, and but recently 
dead, one Samuel Metcalfe. This man, tracing all motion, all 
force to solar fire — Aith, the sun; TJr, fire, iETHEB — spent 
the whole of his fife, much of it in actual want, to prove that 
there was no necessity to conceive two forces in nature, that 
two forces were impossible, and that the idea of two was 
founded purely on the observation of the variations of matter 
when the pervading force was in the active or in the negative 
condition. 
At this moment, when the theory of mere motion as the 
origin of all varieties of force is again becoming the prevailing 
thought, it were almost heresy to re-open a debate, which for 
a period appears, by general consent, to be virtually closed ; 
but I accept the risk, and shall state, therefore, what were 
the precise views of the immortal heretic, whose name I have 
whispered to the reader, respecting sun force. Starting with 
the argument on which nearly all physicists are agreed, that 
