126 DISCOURSE ON THE STUDY 



is possible may be themselves inaccurate, or, at least, 

 stand in need of verification. 



(120.) Here we can only call to our assistance 

 the presumed permanence of the great laws of 

 Nature, with all experience in its favour, and the 

 strong impression we have of the general composure 

 and steadiness of every thing relating to the gigantic 

 mass we inhabit "the great globe itself." In its 

 uniform rotation on its axis, accordingly, we find a 

 standard of time, which nothing has ever given us 

 reason to regard as subject to change, and which, 

 compared with other periods which the revolutions 

 of the planets about the sun afford, has demonstrably 

 undergone none since the earliest history. In the 

 dimensions of the earth we find a natural unit 

 of the measure of space, which possesses in per- 

 fection every quality that can be desired ; and in 

 its attraction combined with its rotation the re- 

 searches of dynamical science have enabled us, 

 through the medium of the pendulum, to obtain 

 another invariable standard, more refined and less 

 obvious, it is true, in its origin, but possessing a 

 great advantage in its capability of ready verification, 

 and therefore easily made to serve as a check on 

 the other. The former, viz. direct measurement 

 of the dimensions of the earth, is the origin of 

 the metre, the French unit of linear measure ; the 

 latter, of the British yard. Theoretically speaking, 

 they are equally eligible ; but when we consider that 

 the quantity directly measured, in the case of the 

 metre, is a length a great many thousand times the 

 final unit, and in the pendulum or yard very nearly 

 the unit itself, there can be no hesitation in giving 



