Mathematicall recreations. Or a collection of sundrie problemes, extracted out of the ancient and moderne philosophers, as secrets in nature, and experiments in arithmeticke, geometrie, cosmographie, horolographie, astronomie, navigation, musicke, opticks, architecture, staticke, machanicks, chimestrie, waterworkes, fireworks, &c. ... Most of which were written first in Greeke and Latine, lately compiled in French, by Henry Van Etten Gent. And now delivered in the English tongue, with the examinations, corrections, and augmentations.

PROBLEM. XIII. To finde the weight of smoake, which is exhaled of any combustible body whatsoever.

LEt it be supposed that a great heape of Fa∣gots, or a load of straw waying 500. l should be fired, it is evident that this grosse substance will bee all inverted into smoake and Ashes: now it seemes that the smoake waighes no∣thing; seeing it is of a thinne substance now delated in the Aire, notwithstanding if it were gathered and reduced into the thic∣kest

that it was at first, it would bee sensibly waighty: waigh therefore the ashes which admit 50 pound, now seeing that the rest of the matter is not lost, but is exhaled into smoke, it must necessarily bee, that the rest of the waight (to wit) 450 pound, must bee the waight of the smoke required.

EXAMINATION.

NOw although it bee thus delivered, yet here may be noted, that a ponderositie in his owne medium is not waightie: for things are sayd to be waighty, when they are out of their place, or medium: and the difference of such gravitie, is according to the motion: the smoke therefore certainely is light being in its true medium (the ayre) if it should change his medi∣um, then would we change our discourse.