XXI.] THE SUN. 371 



ported in the air, it does not remain suspended, but at once 

 falls to the ground : in other words, it is attracted, or pulled, 

 towards the eardi, just as it was attracted or pulled towards 

 the magnet ; though in neither case is there any visible 

 means of attraction. The forcehy which the iron rushes to 

 the magnet is called tnagneiism ; the force by which the iron 

 rushes to the earth is called gravitation} 



It is by virtue of this force of gravitation that bodies upon 

 the surface of the earth possess weight ; and, the nearer 

 bodies on the outside of the earth are to the earth's 

 centre, the greater will be the pull, and the greater there- 

 fore will be their v/eight. In consequence of the 

 earth's spheroidal shape, a body at the equator is more 

 distant from the earth's centre than when at either of 

 the poles. Hence, a given mass of matter, which weighs 

 a pound in London, will weigh rather more than a pound, 

 in the Polar regions, and rather less than a pound, in the 

 equatorial zone. If the same body could be carried into 

 space, and placed aloof from the influence of all gravitation, 

 its weight would entirely disajDpear, though the quantity of 

 matter which it contained would remain unaltered. 



The force of gravitation is by no means confined to the 

 earth, but is an universal force, exerted, in greater or less 

 degree, by every mass of matter in the universe. If two 

 bodies, containing different quantities of matter, are allowed 

 to act upon each other, each attracts and is, in turn, attracted, 

 but not to the same extent. The greater the mass, the 

 greater is the intensity of the attractive force. Now the 

 sun is a gigantic mass of matter, and it tends to pull towards 

 its centre all those bodies, including the earth, which cir- 

 culate around it. At present (October, 1877) astronomers 

 are acquainted with 182 bodies, cdX}^^A planets, which revolve 



' Gravitation, from Lat. gravitas, weight. 



B B 2 



