re)  MucroGRAPHIA, 
To begin therefore, it is manifeft from feveral circumftances; that the 
materiabcaufe of the apparition of thefe feveral Colours, is fomeLamina 
or Plate of atranfparent or pellucid body of a:thickne very determi, — 
‘nate and proportioned according ‘to the greater orlefs reftactive power 
of the pellxctd body. And that thisis fo,abundan¢e of Inftances and-par- 
. ticular Gircumftances will make manifeft.. | 9) > df tins slew 
As foft , if youtake any {mall piece of the: Mufeory-glafs.5.and.with a 
' Needle, or fome other convenient Inftrument, cleave it oftentimes into 
thinnerand thinner Lamina, you fhall find, that till you come:to a deters 
minate thinnefs of them, they fhall all appeartranfparent and colourlefs, 
but if you continue to fplit and divide them further,you thal find at laft, 
that each Plate, »after it comes to fuch a determinate thicknefs, thall ap- 
_ pear moft lovely ting'd orimbued witha determinate colour. If firther, 
‘apy means you fo flaw a pretty thick piece, that one part does begin 
to cleave a little from the other, and between thofe two there be by any 
means gotten fome'pellucid wedium,thole laminated pellucid bodies that 
fill that-fpace, fhallexhibit feveral Rainbows or coloured Lines, the co- 
lours }of which will be difpofed and: ranged: according to the various 
thicknefles of the feveral parts of that Plate. . That this is fo, is yet fur 
ther confrmed:by this Experiment. » — | Yet. 2qo low F 
Rake two fmallpieces of ground and »polifht Looking-glafs-plate, 
each about the bignefs of a fhilling, take thefe two dry , and with your 
et and thumbs prefs them very hard and. clofe together,and you 
fhall find, that when they approacheach other very near, there will ap- 
pear feveral Irifés'or coloured Lines, in the fame manner almoft asin the 
Mufcovy-glafs 3° and you may very eafily change any of the Colours of 
any part of :theinterpofed body, by prefling the Plates clofer and hard-_ 
er together. or leaving them more lax 5 that is,a part which appeared co- 
oe with ; ie Po blew, green, 
-, or the like , ‘by altering the appropinquation of the terminatin 
Places Row that air is st socetiity roltedacemdaieari body, Bieichat 
any other'tranfparent fluid will do much the fame, may betryed by were _ 
ting thofe approximated Surfaces. with Water, orany othertranfparent _ 
-Liquor,and proceeding with it inthe fame manneras you did withthe 
Air and you will find much the like'effedt,, only with this difference; _ 
that thofe compreft bodies, which differ moft, in their refractive quality, 
from the-compreffing bodies, exhibit the moft {trong and vivid tine 
Gtures?” Nor is it neceflary , that this /eminated and tingd body. fhould 
be of a fluid fubftance’, ‘any other fubftance’, provided itbe thin enough 
and tran{parent, doing the famething : thisthe Lamwineof our Aafeovys 
glafshint!5, but it may be confirm'd by multitudes of other Inftances. 
And firft, we (hall find, that even Glafs it telf may, bythehelp of@ 
Lamp, be blown thin enough’ to. produce thefe Phenomena of Coz 
lours: “which Phenomena accidentally epee ‘as I have been’ 
_ attempting -to frame {mall Glafles wich aLamp , didnot alittle furprize 
meat firlt, having never heard or feen any ‘thing of it before # 
though afterwards comparing “it with the’ Phexomenag, I had often 
a! é obferved 
