430 THE YARD, PENDULUM, AND METRE. 



be considered the standard yard of the British empire, 

 it provided for its recovery and reproduction in case of 

 the total destruction or loss of it and all its authentic 

 copies and facsimiles, by a declaration that its length is 

 36 inches, such that 39*13929 of them are equal to the 

 length of a pendulum vibrating seconds in vacuo and at 

 the sea-level, in the latitude of London. The report of 

 the French commissioners also in 1798 which led to the 

 enactment of the metrical system, is careful to state that 

 in the event of the total loss or destruction of all 

 material representatives of the metre its value would be 

 easily recoverable from a numerically specified relation 

 between its length and that of the pendulum vibrating 

 seconds at Paris, which had been determined with great 

 accuracy by Borda, one of the commissioners. So that, 

 practically speaking, in the event of the total destruction, 

 by political convulsions, of every authentic yard and 

 metre (supposing any written record of our existing 

 knowledge to survive them) the metre would have been 

 recovered, not by the laborious and costly process 

 of remeasuring the French meridian arc, but by the in- 

 finitely more summary one of a precise repetition of 

 Borda's experiments and the exact re- application of all 

 his corrections and reductions. 



(i i.) For the reproduction of the English yard, a simi- 

 lar repetition of those experiments in London which led 

 to the adoption of the number 39*13929 in. as the mea- 

 sure of the pendulum would, in such an event, no doubt 

 have been, at that epoch, resorted to; though in depart- 

 ure from the wording of the act, which speaks of a 



