SPECIFIC GRAVITY, OR WEIGHT. 37 



any means we could carry it 4,000 miles abore the earth's surface, irhat would be its 

 weight ? 



Solution: The force of gravity decreases upward, as the square of the distance from 

 the ceuter increases : weight, therefore, will decrease in like proportion. The ilistancc of 

 the body upon the surface of the earth, from the center, is 4,000 miles. Its distance from 

 the center, at a point 4,000 miles above the surface, is S.vOO. The square of J.iM'i ji 

 16,000,000 ; the square of 8,000 is 64,iiOi,000. The weight, therefore, will be diminiehed 

 in the proportion that sixty-four bears to sixteen ; that is, it will be diminished 4ths, or 

 weigh ^th of a pound, or 4 ounces. 



3. What will be the weight of the same body removed 8,000 miles from the earth's 

 gtirface ? 



4. A body on the surface of the earth weighs ten tons : what would he its weight if 

 elevated '2,000 miles above the surface ? 



5. How far above the surface of the earth must a pound weight be carried, to make it 

 weigh one ounce avoirdupois ? 



6. What would a body weighing 800 pounds upon the earth's surface, weigh 1,000 

 miles below the surface ? 



The force of gravity decreases as we descend from the surface into the earth, simply 

 as the distance downward increases. — weight being the measure of gravity, it therefore 

 decreases in the same proportion. The distance from the surface of the earth to the 

 center may be assumed to be 4,000 mUes : 1.000 miles is one fourth of 4,000. The dis- 

 tance being decreased one fourth, the weight is diminished in like proportion, and the 

 body will lose '200 pounds, or its total weight would be 600 pounds. 



7. Suppose a body weigViing Sno pounds upon the stirface of the earth were sunk 3,000 

 miles below the surface : what would be its loss in weight ? 



8 If a mass of iron ore weighs ten tons upon the earth's surface, what would it weigh 

 at the bottom of a mine a mile below the surface ? 



9. "What wiU be the weight of the same mass at the bottom of a mine one half a mile 

 below the earth's surface T 



SECTION II. 



SPECinC GKATITT, OE WEIGHT. 



70. A piece of iron sinks in water, and floats upon quick- 

 senses may the silver. In the first instance, we say the iron sinks because it 

 hl^ d^^°^' ^ heavier than water ; and in the second, it floats, because it 

 is hghter than quicksilver. Iron, therefore, is a heavy body 

 compared with water, and a light body compared with mercury. But in or- 

 dinary language, we always consider iron as a heavy body. The term 

 weight may, therefore, be used in two very different senses, and a body may 

 be at once very light or very heavy according to t'iC sense in which the terms 

 are used. A mass of cork which weighs a ton is very heavy, because its ab- 

 solute weight as indicated by the balance, viz.. 2,000 pounds, is considerable. 

 It is, however, in another sense, a light body, because if compared, bulk f jr 

 bulk, with most other solid substances, its weight is very small. Hence we 

 make a distinction between the absolute, or real weight of a body, and its 

 specific, or comparative weight 



