Page:Philosophical Transactions - Volume 024.djvu/335
(1808)
Vacuo, the Mercury then in the Gage standing at 29 inches 1/2: Upon dropping the first quantity of Powder, (by a quantity is to be understood something more than a Grain weight) its Explosion made a Descent of the Mercury in the Gage about an Inch, undulating very little. The second quantity being let fall, the Mercury subsided about 3/4 of an Inch; and so for several quantities following it descended by pretty equal Stages, till it had faln about 6 or 7 Inches; and it was observ'd, upon every quantity fir'd, the Undulations of the Mercury increas'd. But after it had subsided 6 or 7 Inches from 29 1/2, the several descents of it became less, very little or nothing exceeding 1/2 an Inch, altho the Quantities fir'd were equal; but still the undulations encreas'd, and the Explosions manifestly did so too: Till at last the Receiver seem'd to be in great danger of being blown up by a single Quantity, the Undulations of the Mercury being then augmented to 6 or 7 Inches. Now 26 Quantities or 32 Grains having been fir'd upon the Iron, and the Mercury in the Gage faln to 12 3/4, I diligently attended to observe the Gage, which in 7 minutes had ascended 2 Inches 3/4, the next 5 minutes it arose but once Inch 1/4, and so less successively every 5 minutes, that in an hour and 17 minutes it had attain'd but to 21 Inches, the Iron not being quite cold. At 9 the same night I observed the Gage, and found the Mercury elevated to 22 Inches 1/4, precisely: next morn at 9 it had attain'd to 22 1/2, and so continu'd all that day, the Iron then being reduc'd to the temperature of the outward Air. So that from 12 3/4 to 22 1/2 seems to be the weight or spring of heat equal to about 1/3 of an Atmosphere of Air, which would press the Mercury upon the upper part of the Gage, but equal to such a degree of heat as was then contain'd in the Receiver, when the Gage was faln to 12 3/4: The remaining space from 22 1/2 to 29 1/2 is suppos'd to be supply'd with factitious Air, and answers to about 1/4 part of the Recipients whole Con-tent,