VI 



THE LAW OF EQUILIBEIUM 



THAT objects near the earth's surface seek their low- 

 est center of gravity, or, what is the same thing, 

 their equilibrium, was known long before Newton's 

 time quite as well as it is in ours. Indeed, it may truly be 

 said to have been better understood then than now, for 

 the reason that Newton, in his quest for the solution of the 

 mystery of the tides, introduced a perversion of the law 

 that has ever since obsessed the scientific mind and inci- 

 dentally worked untold injury to the cause of astro- 

 nomical science. This pseudo doctrine of which I speak 

 teaches that bodies lose the power of self -balancing when 

 falling in vacuo, and is founded upon what is commonly 

 known as the vacuum-tube experiment, which is thus suc- 

 cinctly described in Ganot's Physics (Art. 77) : 



Since a body falls to the ground in consequence of the earth's 

 attraction on each of its molecules, it follows that, everything else 

 being the same, all bodies, great and small, light and heavy, ought 

 to fall with equal rapidity, and a lump of sand without cohesion 

 should, during its fall, retain its original form as perfectly as if it 

 were compact stone. The fact that a stone falls more rapidly 

 than a feather is due solely to the unequal resistance opposed by 

 the air to the descent of these bodies ; in a vacuum all bodies fall 

 with equal rapidity. To demonstrate this by experiment a glass 

 tube about two yards long may be taken, having one of its ends 

 completely closed, and a brass cock fixed to the other. After 

 having introduced bodies of different weights and densities 

 (pieces of lead, paper, feather, etc.) into the tube, the air is with- 

 drawn from it by an air pump, and the cock closed. If the tube 

 be now suddenly reversed, all the bodies will fall equally quickly. 

 On introducing a little air and again inverting the tube, the lighter 

 bodies become slightly retarded, and this retardation increases 

 with the quantity of air introduced. 



