OPPOSING MOTIONS. 119 



general law of nature. Where two currents of 

 tide meet at sea, the water is trembling and agi- 

 tated, while a single tide having a greater velocity 

 runs comparatively smooth. When opposing winds 

 strive together upon the face of the waters, the 

 waters are not only thrown into commotion, but a 

 vortex is formed, a cloudy pillar twines upward, 

 and if the striving winds are powerful, and their 

 strife long continued, a cloud may be made to 

 ascend, which may be borne landward, and fall in 

 deluge and devastation, or falling seaward it may 

 scatter navies, and entomb the most gallant ves- 

 sels in the deep. 



So also in smaller matters, opposing the direction 

 of a motion by another motion, gives to the colli- 

 sion the joint force of both. If stopped at the 

 same length, a blow hits harder when received on 

 the advancing arm, than when on the arm at rest ; 

 the shock of one carriage coming into collision 

 with another one from the opposite on a cross 

 direction is much greater than when the one car- 

 riage is standing still ; and that again is greater 

 than if they are both moving one way, and the 

 swift one runs up upon the slow. In all these 

 cases, and in every case that we can examine, the 

 swifter of the two impinging substances produces 

 a proportionally greater effect than the other. 

 Soft iron can be made to move so rapidly as not 

 only to cut hardened steel as freely as a steel saw 

 cuts soft timber, but it can be made to burn the 

 steel as easily as if that were the most inflammable 

 of substances. The purest water of the brooks 

 and streams wears away their channels ; and the 

 winds, which are but the thin air in motion, level 

 the abodes of man with the earth, and sweep the 



