Lectures on natural philosophy the result of many years' practical experience of the facts elucidated. With an appendix: containing, a great number and variety of astronomical and geographical problems. Also some useful tables, and a comprehensive vocabulary / [Margaret Bryan].

  • Margaret Bryan
Date:
1806
Catalogue details

Licence: Public Domain Mark

Credit: Lectures on natural philosophy the result of many years' practical experience of the facts elucidated. With an appendix: containing, a great number and variety of astronomical and geographical problems. Also some useful tables, and a comprehensive vocabulary / [Margaret Bryan]. Source: Wellcome Collection.

    145/510 (page 79)
    ON PROJECTILES. Let us consider for a moment the great advantages derived from the knowledge of the resistance of air, in improving the theory of projectiles. Idie theory of projectiles applied to military purposes is the calculation of the resistance of the atmosphere, in order to know the course a ball will take through the air, and the distance it will range. We might suppose that heavy balls, passing through the air with great velocity, would not meet with any sensible resist- ance : but this is not the case in fact, as the greater the velocity the greater resistance it creates ; for it is known that a liall fired from a cannon which will pass through two miles in air, would range forty miles in vacuum. It is unnecessary for us to enter into the con- sideration of projectiles; I merelj’^ mention them as being connected with tlie subject of resistances. I have treated largely on the laws of motion and gravity in my lectures on Astronomy, so far as relates to the revolutions of the bodies which compose the solar system: but that is foreign to my present purpose; therefore I shall only state the circumstances that are considered in regard to projectiles when employed on terrestrial suljjects, namely, the impressed force, the resistance of the air, and gravity. These are all allowed for in the ballistic art, which renders the theory of projectiles more dif- ficult than any other mathematical calcidation; for, though the effects of gravity arc always alike at the same place and at the same distances from the earth, yet the density of the air varies con- siderably at different times. Of the difficulty attending this cal- culation Ave may form some idea, Avhen Ave knoAV that in gunnery a piece of ordnance must have a certain elevatipn to enable it to convey a ball to a particular spot; that the increasing effects of gravity on it, as it a])})roachcs tlie earth, must be ascertained; the