66 
MicroGRAPHIA., 
pulfe «bis after reflection propagated by ¢ d, cd, equally remote ftom 
each other with 2b, a6, fo that ag*+gc, or bh*hd are either of 
them equal to. 4a,asis alfo cc, but the body BAE being pf ae 
part of the light of this Ray is refraéted in the furface AB, and propa 
gated by gz kh to the furface E F, whence it is refleted and refraéted 
gain by the furface AB. So that after two refractions and one reflection, 
there is propagated a kind of fainter Ray e ~ x f, whofe pulfe isnot on- 
ly weaker by reafon of the two refractions in the furface A B, but by rea- 
on of the time fpent in pafling and repailing between the two furfaces 
AB and EF; ef which isthis fainter or weaker pulfe comes behind the 
pulfe cd; fo that hereby (the furfaces AB, and EF being fo neer toge- 
ther, that the eye cannot di{criminate them from one) this confus'd or 
duplicated pulfe, whofe ftrongeft part precedes, and whofe weakeft fol- 
lows, does produce on the Retiza (or the optick merve that covers the 
bottom of the eye) the fenfation of a YeHow. 
And fecondly, this Ye4ow will appearfo much the deeper, by how 
much the further back towards the middle between cd and cd the fpu- 
rious pulfe ef is remov'd, as in 2 where the furface BC being further 
remov'd from EF, the weaker pulfe ef will be nearer to the middle, and 
will make an impreffion on the eye of a Red. | 
_ But thirdly, if the two refle@ting furfacesbe yet further removd afun- 
der!(as in 3 CD and EF are) thenwill the weaker pulfe befo farr 
behind, that it will be more then half the diftance between ¢d and cd. 
And in this cafe it will rather feem to precede the following ftronger 
pulfe, then to follow the preceding one, and confequently a Blue will be 
generated. And when the weaker pulfe is juft in the middle beween two 
{trong ones, then is a deep and lovely Purple generated ; but when the 
weaker pulfe ef is very neer to cd, then is there generated a Green, _ 
which will be blver, or yelower, according asthe approximate weak pullfe _ 
does precede or follow the ftronger. | aus:\d3 
Now fourthly, ifthe thicker Plate chance to be cleft into two thinner 
Plates, as CDFE isdivided into two Plates by the furface GH then 
from the compofition arifing from the thrée reflections in the furfaces 
CD, GH, and EF, there will be generated feveral compounded or mixt 
colours, which will be very differing, according as the proportion be- 
tween the thicknefles of thofe two divided Plates CDHG, and GHFE 
are varied. : one ero 
And fifthly, if thefe furfaces C D and F E are further remov’d.afundery’ 
the weaker pulfe will yet lage behind much further; and not onely be: 
coincident with the fecond, cd, but lagg behind thatalfo, andthat fo 
f> 
_ much the more, by how much the thicker the Plate be; fo that by de-' 
grees it will be coizcident with the third ¢d backward alfo, and.by de= 
grecs, as the Plate grows thicker with a fourth, and fo onward to afifth, 
h, feventh, or eighth; fo that if there be a thin tranfparent body,that 
from the greateft thinnefs requifite to produce colours, does,intheman- 
ner of a Wedge.by degrees grow to the greateft thicknefs that aPlatecan 
be of,to exhibit a colour by the reflection of Light from fuch a setiege % 
