( 2©45 ) 
4* It is not fo hard, as to endure polifliing Norisiteafily 
conftmed5 r>or reduced into a ^'^/x but by a ftrong fire^ by 
which it will turn into a lubftance like unflaked lirae, which 
will heat a wet finger, and , when fprinkled with fountain- 
water, will buble up, and become like common lime. 
5. -<^5^»/j/or/^ being by me droppd upon it^ it was corro^ 
ded, and thefupeificial parts were put into a motion with 
fome noife. And when 1 pulverized it in a mortar, Aqua 
fortis, powred on it, made it boyle, till all^vas diflbtved.and 
the MefiflrHum tinged with a yellowifh colour. Then put' 
ting it into a T hermometer furniflit with a hollow glafs-balljit 
confiderably (hew'd the difference of Heat and Cold. The 
powder being diflblv'd in y^j'/Z/^/^^r///, I dropp'd fome Spirit 
of Vitriol upon itj to feparate the thick from the thin, and to 
precipitate the white calx to ihebottom» 
6* The fides of this Body are exceeding (inooth , which is 
then eafily obtained, if a thinner piece be nimbly broke afun- 
der with your finger* But if yi)u flirike it with a hammer, 
the percullion hath not the lame effeft upon, nor is equally 
refifted from every parr 5 whe^^ce the fmooth fides of this 
Mineral become often fcabrous. The whole Body is rather 
clear than bright, of the colour of limpid water 3 but that 
colour, when it hath been immerfed in water and dryeda- 
gain, becomes dull* Hence it is, that in its native place the 
upper furface is darkifh, becaufe of the Rains and Snows 
fallen upon it* Sometimes there appear alfo (bme reflefti- 
ous of colours, as in the Rain-bow. The Angles are not 
pointed alike, all the flat fides being obliquely incliaed to 
one another. The oppofite plains'are parallel. 
7* In this Ghryftallin Prifme,two of the plain Angles are al- 
ways acute, and the two other obtufe ; and never any of 
them is equal to the collateral Angles of the Inclinations. 
8. The Ob jefts feen through it^ appear fometimes, and in 
certain pofitions of the Prifme, double: Where *tis to be 
notedjthat thediftance between the two images is greater or 
lefijaccording to the different bignefs of the Prifme^ inforauch 
that iti thinner pieces this difference of the double image al- 
mcft vaniftieth* §*The 
