Page:Philosophical Transactions - Volume 004.djvu/123

 end wiped very clean with cloaths, if then it weigh more than before, 'tis of that kind, which imbibes water, and therefore not lo lit to endure any considerable time without rotting the laths and timber.

4. These Stones may be pretty well guessed at, whether they be of a close or loose texture, by their Colour: For the overblackish Blew is aptest to take in water; but the lighter blew is alwayes the firmest and closest. To which may be added the Touch; for, a good stone feels somewhat hard and rough; whereas an open stone feels very smooth, and as twere, oily.

5. Place your Stone longways perpendicular in the midst of a Vessel of water (no matter, how shallow the water be, so it exceed halfe a foot depth,) and be sure, the upper un-immersed part of the Stone be not accidentally wetted by the hand, or otherwise; and so let it remaine a day, or halfe a day, or less. If it be a good firme stone, it will not draw (as they speak) water above half an inch above the level of the water, and that perhaps but at the edges only, the parts of which might be somewhat loosen'd in the hewing. But a bad stone will draw water up to the very top, be the stone as long as it will, all over.

As for the Charges of Covering Houses with Slate, they may be thus computed.