( ^^74 ) 
worn, and confequently leffen'd in their Spring y fo theXight 
(in proportion to the abatement of their force on theMovfne 
Body,) would be diminifti'd ^ as I have often obferv'd, when 
the Motion has been made for fonie fmall time, only in Vacuo 
or inCommon Air. And had the Experiment been begun 
where it finifti'd, the k0er quantity of Light (from rbe pre- 
mention'd Caufc) would then have been exhibited in Vacuo. 
JHence it follows, That the Different Mediums did no ways 
contribute to the Augmentation or Diminution of the Liehc 
produced, but feems wholly to proceed from the weakening 
of the Springs by the wear of the Bodies, which is be^^ot 
by the violent Attrition of one upon the other in either 
medium*. I do not find that the pollifh, or glaze, on the 
outfide of a Glafs, adds any thing to the Light,' having 
produced the fame by a Glafs much worn by often ufing.. 
I have repeated the fame Experiment about noon in a 
dear day 5 the fuccefs was, that the Light p»- .duc'd in Va- 
cuo was then as fenfible to fight, as a piece of red hot < 
Glafs of the fame bignefs at the fame time would have 
appeared in the open Air. But notwithftanding tlij Ap- 
pearance is fuch, it is no longer fo than fliu Motion is 
continued. Hence it is to be obfervy, Jfaat altho it feems 
to be of the Colour of Red hot, or Melted, yet it is not • 
for were it really fo, it muft of Neceffity fome fmall time 
outlive the Motion 3 which in the darkeft Night I could 
(as yet) never difcovefo 
Expt- 
