B, as Radu^s to the Secant of the ji/^gk of Elevation F G B. 
Thele Profcfuiorss confidered, there is no queftion relating 
to Projeffs, which by the help of tlicm may not eaPJy be 
Solved ; and tho^ it be true tnat moil: of them are to be met 
v/ichal, 'inGdileus,Torrke!iiiis and others^ who have lakea 
them from tao\!c Authors^ yet their Books being i'orreign, 
and not eafy to come by, and their D mo^firations long and 
difficult, I thought it notamiftto give the whole Dotfiine 
here in tnglijhy witii iiicii fhort Andytkal Proof of my own^ 
as might be iufficient to evmce their Truth» 
The Tenth Propofuwn containes a Pr>^ /^»;/^, untouch't by 
Torrkelliusy which is of the greateft ufe in Gfrnf^ery^ d.nd for 
the fake of which this Difcourje was pr.ncipally intended ; It 
was firft Solved by Mr. Anderfon^ m v)s Book of the Genuine 
ufe and elfeds of the Gimn^ Printed in tae Year 167 4 ; but 
his Solution requi cd {(> much Calculation^ that it put me 
upon fearch, wiietber it might not be done more eafiiy^ and 
thereupon in the Year 1678 I found out the rule I njw pub- 
lifh, and from it the Ceometricd ConSlrudion : Since which 
time there has a large Treatife of this Subjed Entituled, Cart 
dejettsrles Bomhes, been Publifhed in France by Monfieur Elm- 
del, wherein he gives the Solutions of this Problem by Mejjie-^ 
P,rs Bout J Romer and de la Hire ; But none of them being the 
lame with mine, or in my Opinion more ealy, and moil of 
them more Operofe, and befides mine finding the T^^/^^^'^/-, 
which generally determines the Angle better than its Strje^ I 
thought my felf obliged to Print it for the ufe of all fuch, as 
defire to be informed iii the M^themAttcd part, ot the Art of 
Gunmry. 
Now thefe rules were rigidly true, were it not, aslfaid 
before, fortheOppofitionof the Medium, whereby not only 
die direO: impreil Motion is continually retarded, by like- 
wife the increafe of the Velxity of the ftll^ fb that the (paces 
delcribed thereby, are not exa£lly as the fquarcs of the times : 
But what this Oppofition of the^/> is, againft fcveral Vdo- 
c'uieSjBtdksj ^i'yl Weights, is not ioeaiy to. determine. Tis 
