1861.] on the Physical Basis of Solar Chemistry. 393 



different tension. Its vibrations are of two distinct kinds ; so also when 

 we have three or more bands, we are to figure as many distinct sets of 

 springs, each set capable of vibrating in its own particular time and at 

 a different rate from the other. If we seize this idea definitely, we shall 

 have no difiiculty in dropping the metaphor of springs, and substituting 

 for it mentally the forces by which the atoms act upon each other. 

 Having thus far cleared our way, let us make another effort to advance. 



Here is a pendulum, — a heavy ivory ball suspended from a string. 

 I blow against this ball ; a single puff of my breath moves it a little 

 way from its position of rest ; it swings back towards me, and when 

 it reaches the limit of its swing I puff again. It now swings further ; 

 and thus by timing my puffs I can so accumulate their action as to 

 produce oscillations of large amplitude. The ivory ball here has 

 absorbed the motions which my breath communicated to the air. I 

 now bring the ball to rest. Suppose, instead of my breath, a wave of 

 air to strike against it, and that this wave is followed by a series of 

 others which succeed each other exactly in the same intervals as my 

 puffs ; it is perfectly manifest that these waves would communicate 

 their motion to the ball and cause it to swing as the puffs did. And 

 it is equally manifest that this would not be the case if the impulses of 

 the waves were not properly timed ; for then the motion imparted to 

 the pendulum by one wave would be neutralized by another, and there 

 could not be that accumulation of effect which we have when the 

 periods of the waves correspond with the periods of the pendulum. 

 So much for the kind of impulses absorbed by the pendulum. But such 

 a pendulum set oscillating in air produces waves in the air ; and we 

 see that the waves which it produces must be of the same period as 

 those whose motions it would take up or absorb most copiously if they 

 struck against it. Just in passing I may remark, that if the periods of 

 the waves be double, treble, quadruple, &c., the periods of the pendulum, 

 the shocks imparted to the latter would also be so timed as to produce 

 an accumulation of motion. 



Perhaps the most curious effect of these timed impulses ever 

 described was that observed by a watchmaker, named EUicott, in the 

 year 1741. He set two clocks leaning against the same rail ; one of 

 them, which we may call A, was set going ; the other, B, not. Some 

 time afterwards he found, to his surprise, that B was ticking also. The 

 pendulums being of the same length the shocks imparted by the tick- 

 ing of A to the rail against which both clocks rested were propagated 

 to B, and were so timed as to set B going. Other curious effects were 

 at the same time observed. When the pendulums differed from each 

 other a certain amount, A set B going, but the re-action of B stopped 

 A. Then B set A going, and the re-action of A stopped B. If the 

 periods of oscillation were close to each other, but still not quite alike, 

 the clocks mutually controlled each other, and by a kind of mutual 

 compromise they ticked in perfect unison. 



But what has all this to do with our present subject ? They are 

 n>echanically identical. The varied actions of the universe are all 



