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# Title: Opticks: Or, A Treatise Of The Reflexions, Refractions, Inflexions and Colours Of Light (shelfmark Leibn. Marg. 193)
# Folio 57, page id 1677894601:0067
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IF any Motion or moving ching wrhacloerer be incident
rich ans relocier on any broad and chin space termina-
ced on boch sides by erro Parallel Planes, and in its paltage
chroush chac space bc urged perpendiculartr corrards the
turcher Plane by any Force irhich at siren distances trom
che Plane is of given quancicies; the perpendicular Velo-
ciey ot chat Mocion or Thing, ac its emergins out of chac
Space, Ball bc alvars equal eo the Square ROOE oF chc
Summ oF che Square ot che perpendicular Velociey ot
ehac Norion Or Thins at ies Incidence on thac space;
and ot che Square ot che perpendicular Velociey irhich
chac Mocion or Thing vould hare ac ies Emergence, il
ac iis Incidence irs perpendicular Velocier as intinicely
licele.
And che same Proxosition holds Erre OF anv. NTOtiOn OF
Fhins perpendicularty recarded in ies pastage chrouoh chac
Space, it instead of the summ ot che ero Squares rou cake
cheir difference. The Demonstration Machemaricians will
calily find out, and cheretore I CalI noc trouble the Rea-
der wich ic.
Suppose nom chac a Ray comins most obliquely in che Fiz. 1.
Line MIC be retracted at C by che Plane RS inco che Line
CHI, and it ic be reguiredt co End che Line CF inco which
any ocher Ray AC ThaII be retracted; let MIC, AD, BC
the sines ot incidence of che tvo RaYS, and NTC, FF, cheir
Sines of Retraction, and lec the equat Morions of che In-
cident Rays be represented by chc equal Lines MI C and
AC, and che Morion MC being considered as parallel to
che retractins Plane, lec the ocher Mocion AC bC distin-
Suihed InEO EIVO NTOtiOnS AD and DC, one ot irhich
AD is parallel, and che orher DC perpendicular to the re
tractino surtace. In like manner, lec the Mocions oF che
emerins Rays be distinguistrd inco cro, Whereot the per-
pendicular