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orange, if not wholly absorbed by the delicacy of its fragrance, 
I may think of a ship ; because in an island where they do not 
grow, a ship is a necessary condition to the presence of an 
orange ; but would any one ever dream therefore of saying that 
an orange was a ship, or a ship was an orange ? In both cases 
there is equally a confounding of things that differ. 
18. He also says that motion is the most obvious of all the affec- 
tions of matter; but force, as force, is not obvious at all. Again, 
he says, “ Visible motion, or relative change of position in space, 
is a phenomenon so obvious to simple apprehension, that to 
attempt to define it would be to render it more obscure.” Yet 
he does define it as “ relative change of position ; '' but what is 
it that is changed in position? We cannot predicate change of 
position of force alone. If there be motion, it must be motion of 
something; but force is not a thing. If we say that motion 
visibly manifests the exercise of force, all is clear; but when we 
confound force with motion, we are lost in a chaos of words. 
19. Mr. Spencer attempts to overturn our definition of Force 
by stating that motion, so far from being distinctly conceivable, 
as Mr. Grove says, is altogether incomprehensible, and adduces 
a very peculiar illustration to prove his point 
20. “ A body impelled by the hand is clearly perceived to move, 
and to move in a definite direction ; there seems at first sight 
no possibility of doubting that its motion is real, or that it is 
towards a given point. Yet it is quite easy to show that we not 
only may be, but usually are, quite wrong in both these 
judgments. Here, for instance, is a ship which, for simplicity's 
sake, we will suppose to be anchored at the equator with her 
head to the west. When the captain walked from stem to 
stern, in what direction does he move ? East is the obvious 
answer ; an answer which for the moment may pass without 
criticism. But now the anchor is heaved, and the vessel sails 
to the west with a velocity equal to that at which the captain 
walks. In what direction does he now move when he goes 
from stem to stern ? You cannot say east, for the vessel is 
carrying him as fast towards the west as he walks to the east ; 
and you cannot say west for the converse reason. In respect 
to surrounding space he is stationary ; though to all on board 
the ship he seems to be moving. But, now, are we quite sure 
of this conclusion ? Is he really stationary ? When we take 
into account the earth's motion round its axis, we find that 
instead of being stationary he is travelling at the rate of 1,000 
miles per hour to the east ; so that neither the perception of one 
who looks at him, nor the inference of one who allows for the 
ship's motion, is anything like the truth. Nor, indeed, on 
further consideration shall we find this revised conclusion to be 
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