OF PROJECTILES.
lya
CHAP. II.
Of the Curve described by Cannon Shot.
H E charges of
powders'for common service
have been already mentioned (150, No. 1 and 2); theobjects against which they are directed should not be ver/high; and to tire with effect, be less than 1000 yards distant :even then the air’s resistance to the lhot is vety great, tho -gh.its effects on the gravitating prinople be almost insensible.When the line of descent is less than 260 feet, and the time ofthe shot's flight not more than 4 leconJs, the shot’s path is acurve or the second kind ; so denominated to distinguish it fromthe cun e of the fourth kind, where the movements-of impul-sion and grav.tation are both greatly affected by the refinance ofthe air. In the Treatise on Powder, it was demonstrated thatthe air’s resistance considerably retarded the movement ofleaden bullets ; and in the last chapter on hydrostatics, theair’s resistance to mihfiry ptqjectiles is exprestcd in pounds.In this chapter we pi opole to determine the Jaw by whichthe air retards the movement communicated by the impel-ling power, in another manner, viz. directly by its forces.
• 156. To solve this problem, w r e. must find experimentallythe scale of spaces paJJ'ed through during the time of an impul~five movement , retarded by the medium that the Jhot Jlies in :the initial velocities may be found by fne method expressedin the last chapter. Hitherto we have only consideredthe effects of the alterations in the state of the atmosphere,on the inflammation and explosion of the powder, and con-sequently on the initial velocities of shot; we wdl now ex-amine now far they can vary the air’s resistance to the shot,and render the former conclusions erroneous.
The barometer will in some degree point out any changesthat may take place, and for greater accuracy, two small,guns may be fired against a homogenous butt, at any distancenot less than j6o yards; to ascertain by the one, if the initial,velocities be constant (149); and by the other, if the air’sresistance continue the fame, An elevated spot should bechosen for these experiments, where, the gun laid horizontally,may be directed to the right or left, that the first grazes
of