new standards of weights and measures. 3 
seconds at various stations, from Unst to Formentara, are 
there detailed. In these experiments M. Biot employed the 
method of Borda, which requires that the absolute length of 
the pendulum should be obtained by actual measurement at 
each station. M. Biot’s observations and mine, both at 
Unst and Leith Fort, were made at the same stations ; and 
M. Biot found, from the mean of fifty-six series, using 
different measuring rods and various pendulums, the length 
of the second pendulum at Unst to be ,994943083 metres, 
and at Leith Fort ,994524453 metres. 
Converting these results into inches of Sir George Shuck- 
burgh’s scale, by taking the length of the metre at 39,37079 
inches, as given in the Philosophical Transactions for 1818, 
we have the length of the seconds pendulum at Unst, after 
reduction to the level of the sea, 39,17176 inches, and at 
Leith Fort 39,15539 inches, the first differing from my 
determination + ,00029, and the latter —,00015 of an inch. 
The difference of results obtained by methods totally dissi- 
milar being so small, and with contrary signs, it may be 
reasonably inferred from them, as well as from what has 
been before advanced, that the length of the pendulum 
vibrating seconds in London has been determined to within 
one ten-thousandth of an inch of the truth. 
From the near agreement of the results of the French and 
English experiments on the length of the pendulum, it may 
be inferred that the length of the French metre, expressed in 
parts of Sir George Shuckburgh’s scale, is probably not 
erroneous one ten thousandth of an inch. 
From an account recently published by Captain Sabine, 
F. R. S. of his valuable experiments for determining the vari- 
