The Birmingham age-herald., 1910-11-04
HOW TO WEIGH THE EARTH
With Cane Piece of Silver Wire Four Leaden Globes and
 Pencil and Paper It Is Easy

an ordinary room. though the room of an ordinary New York flat couldn't hold very much else if the Cavendish appara-
 tus were crowded into any of them. Cavendish's method was an indirect one The force that draws a body to the earth tits weight-is a manifestation of the power known as gravitation. We know how to measure this power, and every body is familiar with its manifestations.
 Everybody, on the earth or off, attracts every other body. The amount of the at traction depends only on the mass of the two bodies that attract each other and the distance between them.
 If you could take two baseballs away from the earth, away from every planet,
 put them out in space millions of miles from any other body, and then leave them. inches or feet or miles apart, they would proceed to move toward each other. The only reason why they wouldn't do so on the surface of the earth Is because the earth is so much bigger than either of them that they would rush toward the earth-would fall, in other words-before they had chance to move toward each other
 Cavendish eliminater the earth as a
 disturbing factor by making his two DuuleS dttTdcI edcn OtHeT III d nOTlZO1ltai direction. The earth's attraction is, of
 course, vertical He took a long thin stick. very light and six feet in length, and suspended 1t horizontally by sl-
 yer wire fastened to It's middle. To each end of the rod he attached little
 balls or knobs of lead.
 The bodies that were to attract these two knobs were two big balls of lead He arranged his apparatus so that at a rfey ha nAtfId 1.,.ix,e 4la To, balls, close up to the knobs at the end of the stick, one on one side of the knob, one on the other side of the knob at the other end.
 He found that when he did thIs each knob drew toward the big. lead ball near it, swinging the wooden rod round on it's wire support. With delicate instru- ments he measured how much the rod and the wire twisted out of place. Thus he could tell what was the force of attraction-the force of gravitation- pulling the knobs toward the lead balls He knew how much the earth would at tract his little knobs-that is he knew their weight; he knew how much ma terial there was in the large lead balls he used, the ratio of the quantity of material in the earth to the quantity in the big balls of lead followed from the simple laws established by Isaac Newton. All the apparatus used is thus comparatively simple-for scientific ex- pertinent at any rate silk or fiber thread can replace the silver wire used by Cavendish, the knobs and balls need not be of lead; they can be of any ma terial-iron. for instance-otherwis the effects of magnetism would overshadow those of gravity. What you have to do is to measure the force that attracts the knobs to the heavy balls, and the
 distance between the knobs and the
 halls. then apply the simple formula of Newton's laws of gravitation.
 The apparatus Is not extremely ac- curate; you will not be able to trust re- suits too far; but when it Is considered that the closest guess of today does not pretend to be within a hundred billion billion tons. and that scientific observers differ by thousands billion billion. there Is some margin to go on. Anywhere be- tween 5,O00,000,0oo and 60o0.oo0,ooo tons.