THE LAW OF EQUILIBRIUM 133 



say, inasmuch as the action of gravity on the balloon, in 

 spite of its act of rising "against gravity/' was legit- 

 imately inferable from the circumstance of the balloon's 

 preserving its lowest center, so the action of the law of 

 equilibrium, in the case of the object in the tube, though 

 masked from our perception behind its high velocity, is 

 reciporocally inferable from the bare fact of the fall? 



How, do you suppose, was the existence of a center of 

 gravity in objects originally discovered? By casually 

 noting the fall of apples from trees? Certainly not ! The 

 unmistakable way was to choose a suitable object, im- 

 merse it in a liquid, and then watch its behavior. To this 

 process two things were essential ; the first being that the 

 object examined be left perf ctly free to turn upon itself ; 

 the second, that it be kept steady enough to allow the eye 

 time and opportunity for critical inspection. 



Now, when Newton came to prove up his tidal theory, 

 he found the knowledge of the law of equilibrium there 

 before him, and he did not find it to his liking; for, as I 

 have previously stated, it did not accord with his major 

 premiss that the moon is the chief tidal force. Most of us 

 have the faults of our virtues, and Newton was no excep- 

 tion. Always fertile in expedients, he was sometimes as 

 inventive in the pursuit of error as he was at other times 

 in the cause of truth. Precisely retracing the course by 

 which the law had originally been brought to light, he one 

 by one systematically restored all the obstacles that 

 aforetime had blocked the road to its unearthing, and, by 

 this unworthy subterfuge, undid discovery and relegated 

 this inestimable diadem of knowledge back again into the 

 limbo of the Unknown. His tube having to be of glass, to 

 ensure transparency, and glass being by nature very fra- 

 gile, it was manifestly impracticable to provide one of even 

 moderate length, so it was actually made but five feet 

 long. Moreover, the tube needing to be hermetically 

 sealed as a necessary condition to the pumping out of the 

 enclosed air, it became automatically impossible to intro- 

 duce instruments for precise measurements^ supposing 

 such exactness to have been desired. Finally came the 



