( 2 1/0 ) 
thinking it likely to improve the Vh^HomnoH^ beyond the 
Lift of Cloath formerly us d for the fame purpofe. This 
Woollen was wrapt about the Arms of the Brafs Spring, 
( defcrib*d in former Experiments, ) and being fcrew'd 
down to its place> gently embrac d the Glafs Globe. 
Thus prepared, and the large Receiver put over all, the 
Pump was wrought, and in a little time had cxhaufted 
the Air from the Receiver : Then the large Wheel being 
turnd, gave 15 Revolutions to the Included Globe, to 
one of its own , in which' fwift motion, rubbing on the 
preracntion d Woollen, a fine Purple Light enfu'd, the in- 
cluded Afparatus being diftinguifhable by it, and continu d 
fo during the Attrition. Upon letting in a little Air, 
both the Light and its Colour did diminifti : And as the 
Air at feveral times was fuffer'd to re-enter the Receiver, 
fo the Light became manifeftly more Pale, and lefs Vivid, 
And even when the Receiver wasrepleat with Air, a 
fmall faint Light did difcover itfelf upon the fame Attri- 
tibn given, as at firft. What is farther obfervable in this 
Experiment was, That the Purple Light which appeared, 
feem'd to be about the breadth of half an Inch, and about 
one in height, being vifible no where but on each Arm of 
the Brafs Spring, where the Glafs in its motion rubb*d on 
the Woollen. That the Light remained fteady without 
the leaft Undulation, notwithftanding the Motion of the 
Glafs was confiderably fwift. This being all that occurred 
at that time, I now beg leave to give fome Account of the 
Various fhmomena that has happened at divers Repetitions 
of the fame Experiment. 
The firft time I made it, its fuccefs was m.uch the fame 
as I have juft now related : But when I came to repeat it 
twice or thrice, with the fame Glafs, no Purple Light ap- 
peared, a pale one then fucceeded in its room, nor all the 
means I ufed could recover it, till I took a new Glafi, 
which *fter I had us'd for the fame purpofe two or three 
time^ 
