The English works of Thomas Hobbes of Malmesbury, Volume 07 (of 11)
Thomas Hobbes · en
But you have not yet done, you say, with these articles. Therefore
(after you had for a while spoken perplextly, conjecturing, not without
just cause, that I could not understand you) you say that to the end I
may the better perceive your meaning, I should take the example
following. “_Let a movent (in the first figure of this chapter) be moved
uniformly in the time A B, with the continual impetus A C, or B I, whose
whole velocity shall therefore be the parallelogram A C I B. And another
movent be uniformly accelerated, so as in the time A B it acquire the
same impetus B I. Now as the whole velocity, is to the whole velocity,
so is the length run over, to the length run over._” All this I
acknowledge to be according to my sense, saving that your putting your
word _movens_ instead of my word _mobile_ hath corrupted this article.
For in the first article, I meddle not with motion by concourse, wherein
only I have to do with two movents to make one motion; but in this I do,
wherein my word is not _movens_ but _mobile_; by which it is easy to
perceive you understand not this proposition. Then you proceed: “_But
the length run over by that accelerated motion is greater than the
length run over by that uniform motion._” Where do I say that? You
answer, “_in the ninth and thirteenth article, in making A B (in the
fifth figure) greater than A C; and A H (in the eighth figure) greater
than A B; and consequently, the triangle A B I, greater than the
parallelogram A C I B_.” That consequently is without consequence; for
it importeth nothing at all in this demonstration, whether A B, or A C
in the fifth figure be the greater. Besides I speak there of the
concourse of two movents, that describe the parabolical line A G D;
where the increasing impetus (because it increaseth as the times) will
be designed by the ordinate lines in the parabola A G D B. And if both
the motions in A B and A C were uniform, the aggregate of the impetus
would be designed by the triangle A B D, which is less than the
parallelogram A C D B. But you thought that the motion made by A C
uniformly, is the same with the motion made uniformly in the same time
by the motions in A B and A C concurring; so likewise, in the eighth
figure, there is nothing hinders A H from being greater than A B, unless
I had said that A B had been described in the time A C with the whole
impetus A C maintained entire; of which there is nothing in the
proposition, nor would at all have been pertinent to it. Therefore all
this new undertaking of the thirteenth, fourteenth, fifteenth, and
sixteenth articles, is to as little purpose as your former objections.
But I perceive that these new and hard speculations, though they turn
the edge of your wit, turn not the edge of your malice.