Analysis of a course of lectures on natural and experimental philosophy. Viz. 1. Magnetism, 2. Mechanics, 3. Chemistry, 4 & 5. Pneumatics, 6. Hydrostatics, 7. Electricity, 8. Fortification, 9. Optics, 10. Use of the globes, & c. 11 and 12. Astronomy / by A. Walker.

  • Walker, A. (Adam), 1730 or 1731-1821.
Date:
[1790]
Catalogue details

Licence: Public Domain Mark

Credit: Analysis of a course of lectures on natural and experimental philosophy. Viz. 1. Magnetism, 2. Mechanics, 3. Chemistry, 4 & 5. Pneumatics, 6. Hydrostatics, 7. Electricity, 8. Fortification, 9. Optics, 10. Use of the globes, & c. 11 and 12. Astronomy / by A. Walker. Source: Wellcome Collection.

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    t >3 ] L E C T U R E II. MECHANICS. THE attraction of gravitation is the weight of bodies, or that tendency which matter has towards the centre: By this power the earth is formed into a denfe ball, and every thing that lives upon it held faft to its furface. A body left to the power of this agent falls about a rood in the firft fecond of time ; three roods in the fecond fecond ; five in the third; feven in the fourth, &c. agreeably to the odd numbers i, 3, 5, 7, 9, 11, 13, &c. For the vis inertia of the falling body, added to the power of gravity in every fucceeding fecond, accelerates it, as the fquares of the times. Thus,—at the end of the 4th fecond the body has fallen about 16 roods,—-at the end of the 6th fecond it has defcended 36 roods, &c. This is proved by a projected ball falling from an horizon¬ tal line one inch in the fame time in which it falls 3, 5, 7, &c. inches in the fucceeding times ; and by the fufpenfion of unequal weights over a pulley. Hence wd find this power of gravity decreafes as the fquares of the diftances increafe, (i.e. a ball, which weighs 91b. on the earth’s furface, would weigh only 1 lb. at three femi-diameters of the earth above it.) For it is found that the moon falls from a tangent to her orbit in this proportion; fhewing that fhe is actuated by the fame law that makes a pebble defcribe a curve when it is thrown from a fling. For that pebble, if it was projected with proper force, and had a vacuum to move through, as the moon has, would go round the earth for ever as file does, Motion is rectilineal; /. e. all bodies put in motion by me force, endeavour to go off in a ftraight line, Hence, if