126 OPPOSING MOTIONS. 



which actually speed in about twenty-four seconds 

 of time, over a distance equal in length to the earth's 

 annual path. Instead, therefore, of being able to 

 question light so as to know whether it be substance 

 or merely motion, we cannot divide time so minutely 

 as to take the slightest note of the duration that it 

 requires to pass from one pole of the earth to the 

 other : and before we can think of the gleam that 

 shoots past us it is millions of miles into the regions 

 of space, shedding its benignant influence upon other 

 and distant worlds. The matter of the earth and 

 also that of the atmosphere, moving so rapidly as 

 they do, and in the direction across the path of the 

 sunbeam, must produce an effect different from that 

 which would result if the earth were at rest and 

 the beam only in motion,; but as we know nothing 

 of either of the two, we cannot compare them or 

 state what phenomena of nature result from the 

 compound motion. There is no doubt, however, 

 that the action is greater than it would be if there 

 were only one motion, because we find that to be a 

 general law of nature. Where two currents of 

 tide meet at sea, the water is trembling and agitated, 

 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 de- 

 vastation, or falling seaward it may scatter navies, 

 and entomb the most gallant vessels 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 ad- 

 vancing arm, than when on the arm at rest: the 

 shock of one carriage coming into collision with 



