417 
nkn mi 5®? ?° m ° the1 ' P ° mts ° f sl S ht > ma ? be equally true, and 
also needful for some purposes of science. But it is sciolism and 
not science, which offers us the motions relative to some distant 
inaccessible point of sight as the absolute motions, and denounces 
an tne rest as unscientific and untrue. 
40. All known and experienced motions are relative. Absolute 
motions, even if they did exist, could never be discovered or known 
I fie question that remains is the comparative use and importance 
ot the different sets of relations. Something or other must be 
assumed to be at rest, and we may adopt either a mechanical, sen- 
sible, or moral standard of the relative value. 
If we take a mechanical standard, we must deal with the 
material atoms alone. Here equal force or mass is the one test of 
value. . Ihe whole earth thus exceeds immensely the mass of any 
mountain or plain on its own surface. The mass of the sun is far 
greater than that of the earth, and the sum total of all the stars in 
the firmament is some thousand times, possibly some millions of 
times, greater still. There will thus be a clear gradation in the 
importance of the relative motions, tried by a mechanical standard, 
Ironi those which have reference to some one locality of the 
earth s surface, to those which relate to an unknown dynamical 
centre of the whole stellar universe. 
41. When we consider motion with reference to the senses and 
faculties of living creatures, a wholly different order of importance 
is revealed. Our earth, on its surface, is peopled with countless 
forms of life. These are wholly absent from the void places of the 
system, and all but the surfaces of the other planets ; and of their 
presence even there we have no assurance. And thus the 
relative motions, as viewed from all places on the earth's surface 
have an importance shared by few, and possibly by none, of the 
countless varieties of sets of such motions, as viewed from other 
points of sight, in their bearing on the sensations and activities of 
the whole world of animated existence. 
42. Again, the mechanical or solid proportion of things, and 
the visual, are not the same. The universe is twofold, as present 
to the eyes of every known living creature. One half belong to 
the skies above, the other to the earth below. The celestial 
hemisphere presents only a few objects, dispersed over its blue 
vault, and these are accessible by one sense alone. But the terrestrial 
half, the earth s surface, is filled in every part with objects that 
come within the range of all the senses, and affect most intimately, 
in various ways, the safety and welfare of every living creature. 
Thus the relative importance of the two visual hemispheres reverses 
that of their absolute dimension or size ; and the ratio of masses 
and momenta, for all the uses of life, has to be displaced and 
superseded by another of a wholly different, and almost opposite 
