— 
and down i fevera 
MrcrROGRAPHIA, 
much better ;, we might much further di(cov er its divifibility. . Nor are 
thefe flakes only regular asto the {moothnefs of their Surfaces; but third- 
ly , In many Plates they may be perceived to be terminated naturally 
with edges of the figure of a Rhowboeid. ThisFigure ismuch more con- 
fpicuous in our Englifhtalk, much whereof is found in the Lead Mines, 
and is¢ommonly called. spar, and Kauck., which is of the fame kind of 
fubftance with the Selenitis, but is feldom found in fo large flakes as that 
is, nor is itcaltcogether fo tuff, but is much more clear and tran{parent,and 
much more curioufly fhaped , and yet may be cleft and flak’d likethe o- 
ther Se/evitis. But fourthly, this ftone hasa property, which in refpeé 
of the Aficrofcepe, ismore notable, and that is, that it exhibits feveral ap- 
ances of Colours, -both tothe naked Eye, but much more:confpicu- 
| otra Microfeepe for the exhibiting of which , I took a piece of 
glafs, and — or cleaving it into thin Plates, [found that up 
parts of them! could plainly perceive feveral white 
fpecks or flaws, and others diverfly coloured with all the Colours of the 
Rainbow; and with the Microfcope could perceive , that thefe Colours 
were ranged in ringsthat incompafied the white {peck or flaw, and were 
round or irregular, according to the fhape of the {pot which they termi- 
nated 5 and the pofition of Colours, in refpect of one another, was the 
y fameasin the Rainbow. The confecution of thofe Colours from the 
niddle of the fpot outward being Blew, Purple, Scarlet, Yellow, Green; 
Blew, Purple, Scarlet, and fo onwards, fometimes half a {core times re- 
peated, that is,there appeared fix,feven,eight.nine or ten feveral coloured 
ringsor lines, each incircling the other, inthe fame manner asI have of- 
ten feen.a very vivid Rainbow to have four or five feveral Rings of Cor - 
jours, thatis, accounting all the Gradations between Red and Blew for 
one: But the orderof the Colours.in thefe Rings was quite contrary to 
the primary or innermoft Raizbom, and the fame with chofeof the fecon- 
dary or outermoft Rainbow ; thefe coloured Linesor Irifés, as Imay fo 
call them, were fome of them much brighter then others , and fome of 
them alfo very much broader, they being fome of them ten,twenty, nay, 
Ibelieve , neer a hundred times broader then others; and thofe ufually 
were broadifh which were necreft the center or middle of the.flaw. And 
oftentimes Ifound , that thefe Colours reacht to the very middle of the 
flaw, and then there appeared in the middle a very large fpot, for the 
moft part, all of one colour , which was very vivid , and all the other 
Coloursincompafling it, gradually afcending, and growing narrower to- 
wards the edges, keeping the fame order , as inthe fecuzdary Rainbow, 
\-that is,if the middle were Blew, the next incompafling it would be a Pur¢ 
 ple,the:third a Red, the fourth a Yellow, cc, as above ; if the middle 
were a Ked,the next without it would be a Yellow,the thirda Green,the 
fourth a Blew,and fo onward,. And this order italwayes_ kept whatfo- 
ever werethemiddleColour, __ | ! 
“There was further obfervable in feveral other parts of this Body, ma- 
ny Linesor Threads,cach of them of fome one peculiar Colour, and thofe 
foexceedingly bright and vivid , that it afforded avery pleafant abe? 
ring : throug 
