The English works of Thomas Hobbes of Malmesbury, Volume 07 (of 11) — Thomas Hobbes — John Shaqi
The English works of Thomas Hobbes of Malmesbury, Volume 07 (of 11)
Thomas Hobbes · en
To the third article, which is this: “_In motu uniformiter a quiete
accelerato_,” _etc._ “_In motion uniformly accelerated from rest, that
is, when the impetus increaseth in proportion to the times, the length
run over in one time is to the length run over in another time, as the
product of the impetus multiplied by the time, to the product of the
impetus multiplied by the time_;” you object, “_that the lengths run
over are in that proportion which the impetus hath to the impetus; not
that which the impetus hath to the time, because impetus to time has no
proportion, as being heterogeneous_.” First, when you say the impetus,
do you mean some one impetus designed by some one of the unequal
straight lines parallel to the base B I? That is manifestly false. You
mean the aggregate of all those unequal parallels. But that is the same
thing with the time multiplied into the mean impetus. And so you say the
same that I do. Again, I ask, where it is that I say or dream that the
lengths run over are in the proportion of the impetus to the times? Is
it you or I that dream? And for your heterogeneity of the quantities of
time and of swiftness, I have already in divers places showed you your
error. Again, why do you make B I represent the lengths run over, which
I make to be represented by D E, a line taken at pleasure; and you also
a few lines before make the same B I to design the greatest acquired
impetus? These are things which show that you are puzzled and entangled
with the unusual speculation of time and motion, and yet are thrust on
with pride and spite to adventure upon the examination of this chapter.
Secondly, you grant the demonstration to be good, supposing I mean it,
as I seem to speak, of one and the same motion. But why do I not mean it
of one and the same motion, when I say not in _motions_, but in _motion_
uniform? _Because_, say you, _in that which follows, I draw it also to
different motions_. You should have given at least one instance of it;
but there is no such matter. And yet the proposition is in that case
also true; though then it must not be demonstrated by the similitude of
triangles, as in the case present. And therefore the objections you make
from different impetus acquired in the same time, and from other cases
which you mention, are nothing worth.