MicROGRAPHYA, 
And that this is fo, a little clofer examination of the Phexénena and 
the. Figure of the body, by this'Hypothefis, willmake evidents.( . >.> 
For firft (as we have already obferved) the /eminated body mukt be 
of a.determinate thicknefs, that is, it muft not be thinnerthen ha de: 
terminate quantity; for] have always obferv’d, that. neer the edges 
of thofe which are exceeding thin, the colouts difappear, and the part 
grows white; nor miuft it be thicker then anotlier determinate quantity 3 
for I have likewife obferv'd, that beyond fucha thicknefs,no colours ap- 
pear, but the Plate looked white, between which twordeterminate 
thicknefles were al] the colour'd Rings; of which in fome fubftances I 
have:found ten or twelve, in others not half fo many, which I fuppofe des 
_ pends much upon: the tran{parency of the laminated body.-‘Thus:though 
the confecutions are the {ame in the feumm or the fkin on the top of mes 
tals; yet in thofe confecutions the fame. colour is not fo often repeated 
as in the confecutions iu thin Glas, or im Sope-water, or any other more 
tranfparentand glutinous liquor; for in thefe I haveobferv'd, Red; tel- 
lom, Green, Blue, Purples, Red,Yelow,Green,Blue, Purples Red,xellow Green; 
Blue, Purple 5 Red, Yellow, &c. to faceeed. each other,ten or twelve times; 
oa in the other more opacous bodies the confecutions will not be half 
O many. no a an : itv 
- And therefore fecondly, the laminated body muft be tranfparent,and 
this Largue from this,that I have not been able to produce any colour 
at all with an epacous body,though never fo thin, And this\} have often 
try d, by preffing a {mall Glebwle of Atercury between two fmootl: Plates 
of Glafs, whereby Lhave reduc'd. that body to:2 much greater thintiels 
then was requifite to exhibit the colours witha tranfparene, Body.) 
_ Thirdly,there muft be a confiderable refleéting body adjacent tothe 
under or further fide of the /amina or plate: for this Lalways found,that 
the greater that reflection was, the more vivid were the appearing 
colours. 1390 n 10 abeoa1q 229b 
» From which Obfervations,it is moft evident,that the refleétion fromthe 
under or farther fide of the bodyisthe principal caufe of the prodnctionof 
thefe colours 3 which,that it #3 {o,and how it conduces to thateffett,I fhall 
further explain in the following Figure,which is heredefcribed of a very 
great thicknefs, asifit had been view d through the Jicrofeope 3 agg ‘us 
indeed much thicker’ than any AGcrofCope(I have yet us’d has been able to 
fhew me thofe colour’d plates of Glafs, or A4u/covie-glafs, which bhave niet. 
without much trouble view’ d withit ; for though! have endeavoured to 
magnifie them as muchi as the Glafles wete capable of, yet are they fo ex 
ing thin, that I have not hitherto beem able pofitively to determine 
their thicknefs.. This Figure therefore I here reprefenty is'wholy Hy- 
pothetical. > DIR VAS s Sy a. 2 
Let ABCDHFE in the fixth Figure be:a fraffuat of Atufcony-glaft 
thinner toward the end AE, shchehin ier downed’ EDP, “Let us firft fap- 
pofe the: Ray ae sib coming from the Sun, or fome remote: luminous 
ject to fall obdiqnely on the thinner plate BAF, part therefore is re 
flected back by «ghd, the frit. superfici <5 whicuebip see perpendicalae 
ee pulfe 
> yg iti 
65 
