C 88 3 
well as that of Bolognia , will not imbibe Light, while 
they are warm 5 and this laft does not appear fo lu- 
minous when firft prepared, as when it has been fo 
fome time. 
The natural Phofphori do not differ only in the 
before- mention'd Particulars, but alfo in the Colour 
of the Light itfelf. The Light of the natural gene- 
rally appears either perfectly bright, or fomewhat in- 
clining to yellow : The artificial produces a red, and 
fometimes a brown Light ; but there are fome Ex~- 
ceptions to both thefe Rules. From thefe different 
Appearances, the Author conjectures, that there are 
two Sorts of Fire arifing from different Principles * 
that in torrefied Subftances, from a fulphureous, 
and that of the natural, from a terreftrial Principle. 
In obferving a Piece of Lapis Tut'ue , which was 
rough and unequal on its convex Side, fmooth and 
fomewhat polifhed on the concave } he found, to 
his Surprize, that the rough Side was luminous, and 
the fmooth one not. He was very defirous of in- 
veftigating the Caufe of this Appearance. He remem- 
ber'd that fome polifh’d Marbles did not imbibe Light, 
or very little, and that at their Edges ; but, having loft 
their Polifh, they did admit and retain it. He there- 
fore conjectures, that Bodies, according to the Dif- 
pofition of their Surfaces for the Reflexion of the 
Light, either fuffer or prevent its Entrance into them. 
If this Pofition holds good in the Reflection, why 
fhould it not with regard to the Refraction? Our 
Author produces two Experiments, which he appre- 
hends not foreign to the prefent Purpofe; but is yet 
making others, for his further Satisfaction. He ex- 
pofed a glafs Bottle full of Well-Water to the Light, 
and. 
