Page:Philosophical Transactions - Volume 024.djvu/668

withdrawn, the Quicksilver in the Gage was Elevated to 29 Inches and a half. Then suffering some Air to re-enter the Receiver by the Cock, the Mercury in the Gage descended, and made several Vibrations before it became stagnant: In all which it appear'd Luminous only whilst Descending, till the Quicksilver was Purposely Broke by a Violent Agitation of it. Then the Separate Parts appear'd Light on their under Surfaces, which became Concaves during their Ascending, as the other were when they exhibited their Light Descending: The Convex Surfaces being always opake. These Appearances continu'd upon every admission of Air, till near half was admitted. But after that, tho the Mercury had the same Motion given it as before, yet no manner of Light did ensue. Hence it readily concludes, that notwithstanding the Mercurial Phosphorus in the Torricillian Experiment, is not produceable in so dense a Medium as Common Air; so on the other hand, it requires a Medium not so Thin by much as the nearest approach to a Vacuum to Effect it.

Having provided some Quicksilver, very fine, and free from the least Appearance of Soil on its Surface, the Glass which held it being likewise very Clean and Dry; which Glass, with the Contain'd Mercury was Included within a Receiver on the Plate of the Pump, (in form of Fig. the 3d,) From which I presently began to withdraw the Air. But before it was quite Exhausted, (the Mercury in the Gage not exceeding 28 Inches, the Barometer at the same time standing at 29 Inches and a half) the Pump was shaken, by which means the Mercury in the Included Glass being put in Motion, exhibited such a Light, thatnot