A compendium of astronomy; containing the elements of the science, familiarly explained and illustrated, with the latest discoveriesAdapted to the use of schools and academies, and of the general reader . or load stone, theneedle will fly towards the ball,and cling to its surface, to which-ever side of the ball it is present-ed. (Fig. 24.) From this uni-versal descent of bodies near theearth, we infer the existence ofsome force which draws or impels them, and this invisi-ble force we call the attraction of gravitation, or simplygravity. 123. By the laws of gravity we mean the manner inwhich it
A compendium of astronomy; containing the elements of the science, familiarly explained and illustrated, with the latest discoveriesAdapted to the use of schools and academies, and of the general reader . or load stone, theneedle will fly towards the ball,and cling to its surface, to which-ever side of the ball it is present-ed. (Fig. 24.) From this uni-versal descent of bodies near theearth, we infer the existence ofsome force which draws or impels them, and this invisi-ble force we call the attraction of gravitation, or simplygravity. 123. By the laws of gravity we mean the manner inwhich it always acts. They are three in number, andare comprehended in the following proposition : Gravity acts on all matter alike, with a force propor-tioned to the quantity of matter, and inversely as thesquare of the distance. First, gravity acts on all matter alike. Every bodyin nature, whether great or small, whether solid, liquid,or aeriform, exhibits the same tendency to fall towardsthe center of the earth. Some bodies, indeed, seem lessprone to fall than others, and some even appear to rise,as smoke and light vapors. But this is because they aresupported by the air; when that is removed, they de-. 122. In what directions do bodies fall in all parts of theearth ? Illustrate by figure 24. What is gravity ? LAWS OF GRAVITY. 93 scend alike towards the earth; a guinea and a feather,the lightest vapor and the heaviest rocks, fall with equalvelocities. Secondly, the force of gravity is proportioned to thequantity of matter. A mass of lead contains perhapsfifty times as much matter as an equal bulk of cotton ;yet, if carried beyond the atmosphere, and let fall in ab-solute space/they would both descend towards the earthwith equal speed, until they entered the atmosphere,and were the atmosphere removed they would continueto fall side by side until they reached the earth. Nowif the lead contains fifty times as much matter as thecotton, it must take fifty times the force to make it movew
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Keywords: ., bookcentury1800, bookdecade1850, booksubjectastronomy, bookyear18
