Experiment IV. 
Tonchlng the ProdnSfwn of a Confid^rdk Lights upon the 
Attrition of GUfs on Glafi in Vacuo, and in Common 
Air. 
For this Experiment I made ufe of a Globular Glafs, 
about three Inches Diameter, fixt on the Spindle, ( as in 
the laft, ) and to the two Arms of the Brafs Spring ( taken 
notice of in the fame ) were ty'd two flips of thin Board ^ 
to each of which wete firft faftend two pieces of Glafs 
Tube, by putting fome fmall Neal'd Wires through their 
Cavities, which Wires likewife palling through fome holes 
of the Board made for that purpofe, kept them tight in 
their places, ( in form of Fig, 5.) In this Mode, being 
cover'd with a large Receiver, and fitted in all rcfpefts as 
ufual, the Pump was wrought 5 which in a little time had 
exhaufted the Air from it. Then upon turning the large 
Wheel, a f wife Motion was given to the included Glafs 
Globe, in which Motion, rubbing on the premenrion'd 
Tubes, a con(!derable Light was exhibited : The whole 
Included Appar<ttuf became perfeftly diftinguiftiable by it, 
and would have been much more fo, had not the Day- 
light prevented : It then being but very little after 5. P. M. 
a clear Horizon, and in an open Room, when the Expe- 
riment was made. The Colour of the Light produced re- 
fembled Melted Glafs, not only juft on the parts where the 
friftion was made, but feemingly likewife at the Extreams 
of the Tubes A. B. where the Globe in its motion toucht 
them not. 
What farther Obfervable in this Experiment was. That 
upon fuffering the Air to re-enter the Recipient at feveral 
times, at every of which, the Motion being given, as at 
firft,. no lenfible Decay of Light, or Colour of v -^ppear'd, 
excepting at laft, when the Tubes by much rubbing, became 
I i i i i i i i i i J i i worn. 
