256 PHILOSOPHICAL TRANSACTIONS. [aNNO 3 705. 



given it as before, yet no light ensued. Hence it readily appears, that notwith- 

 standing the mercurial phosphorus in the Torricellian experiment is not pro- 

 ducible in so dense a medium as common air; so on the other hand, it re- 

 quires a medium not so thin by much as the nearest approach to a vacuum to 

 effect it. 



ExPER. IV. Showing that a coiuiderable Light may be produced froin Mercury 

 in a Glass, by giving it Motion before the Receiver is quite exhausted. — Havins^ 

 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 ; the 

 glass, with the contained mercury, was included within a receiver on the plate 

 of the pump, in form of fig. 20, from which I presently began to exhaust the 

 air. But before it was quite exhausted (the mercury in the gauge not exceeding 

 28 inches, the barometer at the same time standing at 29 inches and a halt), 

 the pump was shaken, by which means the mercury in the included glass, be- 

 ing put in motion, exhibited such a light, that not only the receiver and in- 

 cluded glass were distinguishable by it, but hands and fingers on the outside 

 were so too. It is to be observed, that though the quicksilver would give a 

 light on a small motion, yet the light was increased by the increasing that mo- 

 tion. What farther occurred was, that when a pretty brisk agitation was given 

 to the mercury, it would resemble waves of light breaking on the sides of the 

 glass, scattering some species of the same appearance towards the upper part of 

 it: that on repeating the experiment three or four times, the phosphorus 

 seemed every time to be more vivid than before, till at last, by often shaking 

 the quicksilver, its surface became something solid, rendering the light less 

 then, than it had been before: that in this, as well as in all other mercurial ex- 

 periments, the light exhibited is of a very pale colour: that the first appearance 

 of this light, is when about half the air contained in the recipient is exhausted, 

 which still increases with the rarefaction ; and confirms, with all the rest, the 

 necessity of air rarefied to such a degree as to produce the mercurial phosphorus, 

 concurring with that made by the motion of the quicksilver in the weather- 

 glass. 



ExPER. V. Showing very odd Flashes of Light, on the repetition of the 

 Experiment, resembling a Shower of Fire. — The account already given of this 

 experiment, so far as occurred at the first time of making, leaves but little 

 room to add more. However, although but little, it is deserving of further 

 notice: its appearance being not only very surprising, but distinguishably the 

 clearest and most vivid light in all the mercurial phosphori, produced in rarefied 

 air. On repeating the 2d experiment, the mercury not only appeared like a 

 shower of fire, but from the crown of the included glass were frequently darted 



