XXIII
cularly downwards we have always to add the projectile force
to the space through which it would have traversed according to
gravity, f.e. if the projectile force is 10‘ per second.
the space for the 3rd second = 5.5 + 10 = 35;
“ “ 3 seconds = 9.5 +3.10 = 75.
§ 50. b) If a body is thrown vertically upwards we have
to subtract from the projectile force the space through which
the body would have fallen by gravity in the given time. As
soon as the projectile force is consumed in doing so, the body
falls as usual.
§ 51. c.) A body thrown horizontally goes as far as if
acted upon only by this projectile force, but it will be always so
much below the original line of projection as it would have
fallen during this time by vertical motion. Thus the body moves
in a curved line (part of a parabola). This is the way, the ball
of a gun passes. What for the aim with a gun? Why not neces
sary at a small distance, why raised at a great distance?
§ 52. d) A body thrown obliquely takes the course of a
parabola, why? In practice the re
sistance of the air must be taken
into consideration (Artillery). Care
ful investigations and calculations
about projections are made in the ballistic science.
§. 53. 3) Pendulum. The motion of the pendulum is a
kind of fall followed by a rise, which is due to inertia, the fall is
accelerated and the rise retarded by gravity.
§ 54. The chief laws are:
1) The oscillations of one and the same pendulum are made
in equal times (are isochronous). Without friction and resis
tance of the air the pendulum would never cease to swing.
2) The durations of the oscillations are in proportion to the
