AFRICA. 229 ' 
the objeft at which he alms be fituated in an 
horizontal diredion. 
In this cafe, nnlefs the dlftancebe very fhort, 
the arrow cannot go point-blank to the mark ; 
but, to hit it, muft defcribe a parabola, to de- 
termine the elements of which requires a com- 
plicated calculation. 
Another neceffary point to be confidered is, 
the exad: force that muft be given to the ar- 
row, that it may neither go beyond nor fall 
fliort of the mark. 
Finally, a third indifpenfable circumftance 
to be known is the, altitude of the curve, that 
is to fay, the compound refult of the force and 
diftance. 
To explain myfelf more clearly : — Suppofe 
the mark be a hundred and fifty feet diftance ; 
in this cafe the lefs radius of the parabola, 
whatever be its extent, muft have one third of 
the length of the greater diameter ; or, in other 
words, the moft elevated point of the courfe of 
the arrow muft be fifty feet. It is neceffary 
too, that this point divide the diameter of the 
diftance nearly into two equal parts ; fince, if 
;he arrov/ furmount this point, it will go be- 
0.3 yond 
