Page:Mathematical collections and translations, in two tomes - Salusbury (1661).djvu/168

 I will not consent that our Poem should be so confined to that unity, as not to leave us fields open for Epsody's, which every smalllsmall [sic] connection should suffice to introduce; but with almost as much liberryliberty [sic] as if we were met to tell stories, it shall be lawful for me to speak, what ever your discourse brings into my mind.

I like this motion very well; and since we are at this liberty, let me take leave, before we passe any farther to ask of you Salviatus, whether you did ever consider what that line may be that is described by the grave moveable naturally falling down from the top of a Tower; and if you have reflected on it, be pleased to tell me what you think thereof.

I have sometimes considered of it, and make no question, that if one could be certain of the nature of that motion wherewith the grave body descendeth to approach the centre of the Terrestrial Globe, mixing it self afterwards with the common circular motion of the diurnal conversion; it might be exactly found what kind of line that is, that the centre of gravity of the moveable describeth in those two motions.

Touching the simple motion towards the centre dependent on the gravity, I think that one may confidently, without error, believe that it is by a right line, as it would be, were the Earth immoveable.

As to this particular, we may not onely believe it, but experience rendereth us certain of the same.

But how doth experience assure us thereof, if we never see any motions but such as are composed of the two, circular and descending.

Nay rather Sagredus we onely see the simple motion of descent; since that other circular one common to the Earth, the Tower and our selves remains imperceptible, and as if it never were, and there remaineth perceptible to us that of the stone, onely not participated by us, and for this, sense demonstrateth that it is by a right line, ever parallel to the said Tower, which is built upright and perpendicular upon the Terrestrial surface.

You are in the right; and this was but too plainly demonstrated to me even now, seeing that I could not remember so easie a thing; but this being so manifest, what more is it that you say you desire, for understanding the nature of this motion downwards?

It sufficeth not to know that it is streight, but its requisite to know whether it be uniform, or irregular; that is, whether it maintain alwayes one and the same velocity, or else goeth retarding or accelerating.

It is already clear, that it goeth continually accellerating.