withdrawn, the Quickfilver in the Gage was Elevated to- 
29 Inches and a half. Then fufFering fome Air to re-enter 
the Receiver by the Cock, the Mercury in the Gage de- 
fftended, and made feveral Vibrations before it became 
ftagnant; In all which it appeared Luminous only whilft 
Defcending, till the Quickfilver was Purpofely Broke by a 
Violent Agitation of it. Tlien the Separate Parts appeared 
Light on their under Surfaces^ which became Concaves 
during theij Afcending, as the other were when ttiiey ex- 
hibited their Light Defcending: The Convex Surfaces be- 
ing always opake*. Thefe Appearances continued upon 
every admifSon of Air^ till near half was admitted. But 
after tbat, tho the Mercury had the fame Motion given it , 
as before,, yet no manner of Light did enfue. Hence it 
readily concludes.,, that notwichftanding the Mercurial 
'P koff horns , in ^ tht TorricillUtj Experiment, is not produce- 
«ble in fo dcn(e siMedin;^ as Common Air 3 fo on the other 
hand, it requires a Medium not (o Thin by much as the 
aeareft approach to a Vacuum to EfFeft it. 
Experiment IV. 
^tvphig that a Cofjfidcrable Light may be Producd from Mcr^ 
cury in a Glafs^ by givifig it Motion before the Receiver k 
qmte Upchm^^d, 
H Y^vi^g provided Tome Quickftlver, very fine; and free 
from the leaft Appearance pf Soil on its Surface, the 
Glafs wliich held it being likewife very Clean and Dry 5 
which Glafs, with the Contain'd Mercury was Included 
within a Receiver on the Place of the Pump, ( in form of 
the 3d,) From which I prefently began to witlidraw 
the Air. But before icAvas qui e Exhaurtec*, (the Mercury 
in the Gage not exceeding 28 i ches, the mrometerat the 
fame time ftanding at 29 Inch :s and a. half) 'Xhe Pump 
was (h iken, by which means ihe Mercury in the Included 
^afs^bcjng put in Motion^^ exhibited fuch a Light, that 
