Page:Philosophical Transactions - Volume 024.djvu/709

Attrition. Likewise between every Bead was ty'd over a String from Pin to Pin, which were so many pieces of small Wire, drove thro the Wood for their better security and fastness, the Beads appearing about half their Diameter beyond the Wood to which they were fixt. (as in Fig. 2.) In this manner it was put on the Spindle, and fasten'd there by the two Nutts, as before describ'd. (See Fig. 3.) Then the Brass Plate on which the Woollen was wrapt, being screw'd to its place, (by means of the Socket, which receives the lower point of the Spindle) would then spring back, and embrace the Amber with a moderate force. (as in Fig. 3.) Thus prepar'd, and the Receiver plac'd over, with its upper Plate and Box for the Spindle to pass through, the Pump was set on work, and in a very little time the Mercury in the Gage was elevated to about 29 inches and a half, which shew'd the Recipient to be well exhausted of its Air. The Great Wheel being then turn'd, gave a very swift Attrition of the Amber on the Woollen, but no Light at first appear'd: Yet in a second or two of time it became visible enough; which shews it requires some degrees of Heat to produce the Phænomenon. I could not observe that the Continuance or Encrease of the Motion, did contribute any thing to the Enhancement of the Light, after the first production of it: Nor would the Light thus produc'd, live on the Amber to continue a Circle, notwithstanding the velocity of the Motion given; but dy'd so soon as it had deserted the Affricated Woollen. However, on the Woollen, (during the Motion,) where the Attrition of the Amber was made, the Light continu'd without Intermission, and was discernible at three or four foot distance. What farther to be taken notice of in this Experiment was, That it highly Corroborates and Confirms those made on the Production of Heat in Vacuo by Attrition: For the Amber was not only moderately heated, but appear'd to be burnt and crackt by the Intenseness of it. And the Woollenagainst