THE YARD, PENDULUM, AND METRE. 427 



by these conditions. Supposing the foot of the most re- 

 markable person who ever lived to be marked out on 

 steel or adamant, it would be at the mercy of fire, earth- 

 quake, loss in political convulsions, and a hundred other 

 forms of destruction or disappearance, without the pos- 

 sibility of reappeal to the original form. Of human 

 works, the most permanent, no doubt, and the most im- 

 posing as well as generally interesting and respected, are 

 those mighty monumental structures which have been 

 erected as if for the purpose of defying the powers of 

 elementary change. Take the vastest of them that to 

 which appeal has been often made for this very purpose 

 the great pyramid of Cheops. When built it was 481 

 ft. in height, and the square area of its base was 764 ft. 

 in the. side. The height is now only 451 ft. and the side 

 of the base only 746 ; and the sole means by which we 

 are now enabled to determine the original height consists 

 in a block of the exterior marble casing which will in 

 all probability disappear in the hands of " the curious " 

 within the next century. Nature presents to us but one 

 material object which combines all the requisites enumer- 

 ated, and combines them all in perfection viz. : the 

 globe itself that we inhabit. And in that' globe we find 

 only two naturally-defined lengths which unite the re- 

 quisites of individuality to identify them under every 

 change of human relations and even of geological revol- 

 utions and catastrophes, and of universality, so as to 

 stand m the same relation to both hemispheres and to 

 all meridians viz. : the earth's polar axis, and its 

 equatorial circumference. For the latter, the equatorial 



