MOTION, LIGHT, AND HEAT. 125 



vessels would be out of the question ; but still, as we 

 have no occasion to lift large fleets or entire hills, 

 for we take hold of other natural principles, and 

 make the fleets sail, and dig through the hills, or 

 break them up piece and piece by gunpowder, we 

 can have cylinders for water-presses as strong as 

 we have any use for. But nature is not limited in 

 her instruments or operations as we are. We are 

 spectators, and can only imitate that which we have 

 found out ; whereas that which we call nature is the 

 thing itself which we observe, all substances and 

 all their properties. Thus, in the resistance of pres- 

 sure, nature can have her apparatus strong, up even 

 to the tearing asunder even the globe itself; and we 

 know not how many powers in addition to those 

 with which we are acquainted there may be linked 

 together to prevent that catastrophe ; but we do 

 know that if a carriage-wheel, made of the toughest 

 iron, were made to trundle round at any thing nearly 

 equal to the rate at which the earth moves, it would 

 not only be in a moment scattered to atoms, but 

 those atoms would speed away on fire, burning and 

 being burnt with more intensity than any furnace 

 that we could kindle or even imagine as being heated 

 by all the art of the founder, and spread conflagra- 

 tion far and wide. Yet that motion of the earth 

 bends not the slightest thread which the little spider 

 spins from stubble to stubble in the autumnal field; 

 and it is as silent as if the mighty careering mass 

 were in a state of perfect repose. 



What effect the rapid motions of the earth may 

 have upon light and heat is quite another matter ; 

 but it is a matter so exquisitely nice and delicate 

 that it will not come at all within the range of our 

 observation. If the earth will not pause in its 

 path round the sun until we can find out the general 

 influence which its motions have upon the creatures 

 on its surface, and their phenomena, much less can 

 we hope to question the march of the sunbeams, 

 L 2 



