Experimental philosophy, in three books containing new experiments microscopical, mercurial, magnetical : with some deductions, and probable hypotheses, raised from them, in avouchment and illustration of the now famous atomical hypothesis / by Henry Power ...

Experiment 5.

THe Collyers tell us, That if a Pistol be shot off in a head remote from the eye of a pit, it will give but a little report, or rather a sudden thump, like a Gun shot off at a great distance; but if it be discharg'd at the eye of the pit in the bottom, it will make a greater noise than if shot off above-ground. But these Experiments are of a dangerous trial in our pits, and the Collyers dare not attempt them by reason of the craziness of the roof of their works, which often falls in of its own accord with∣out any Concussion at all.

Every Cole-pit hath its Vent-pit digg'd down at a competent distance from it, as 50. or 80. paces one from another.

They dig a Vault under-ground from one pit to an∣other (which they call the Vent-pit) that the Ayr may have a free passage from the one pit to the other; so that both pits with that Subterraneous intercourse, or vault, do exactly represent a Syphon invers'd. Now the Ayr always has a Motion, and runs in a stream from one pit to the other; for if the Ayr should have no Motion (or Vent, as they call it) but Restagnate, then they could not work in the pits.

It is not requisite that the Vent-pit should be as deep as the Cole-pit.

Now the Vent, or Current, of Subterraneous Ayr is sometimes one way, and sometimes another; sometimes from the Vent-pit to the Cole-pit, and sometimes con∣trariwise (as the Winds (above ground) do alter;) and also weaker and stronger at sometimes than at others: and sometimes the Vent plays so weakly, that they can∣not work for want of Ventilation.

Then to gather Vent (as they call it) they straiten the Vault, and wall part of it up; so that the Ayr (which before run in a large stream) being now crowded into a lesser channel, and forced to pass through a narrower room, gathers in strength, and runs more swiftly.

Now it is observ'd, that the Subterraneous Ayr is alwayes warm, and in the coldest weather, the warmest; so that it never freezes in that pit, out of which the Vent plays.