76 Mr Troughton on the Length tf the Pendulum. 
Now, the length of the pendulum, as obtained by Captain 
Kater, is S9.1S86, at the temperature of 62° ; but Mr Trough- 
ton has proposed a slight correction upon this length, for the 
follo^dng reasons. 
Captain KateCs pendulum was composed of three dilferent 
kinds of brass, as stated in the following tabic. 
Part of the Pendulum. 
Weight in Air. 
Specific Gravity. 
lb. 
3 weights (cast-brass, ...... 
3.13 
8.417 
4 knee pieces (cast-brass). 
3.14 
7,816 
Bar plate brass, 
3.30 
8.532 
From these numbers Captain Kater deduces 8.469 as the spe- 
cific gravity of the pendulum, and uses this number in his calcu- 
lations ; but, it is obvious, that the true mean of the above speci- 
fic gravities, taking into account both the quantity and quality 
of the brass, is only 8.2601. Beside this circumstance, Captain 
Kater has omitted to carry the deal ends of his apparatus to the 
account of buoyancy. When these two sources of error were 
calculated by Mr Troughton, he found their amount to be 
0.00017, vdiich, added to 39.13860, gives S9.1S877 for the true 
result of Captain Kater’s experiments. Hence, we have, 
Whitehursfs length of the pendulum corrected, S9.13916 
Captain Kater’s length of the pendulum corrected, 39.13877 
Difference, 0.00039 
If Captain Kater’s table of specific gravities is -wi'cng print- 
ed, as Mr Troughton suspects, from the circumstance that 
no 'workman was likely to use brass so porous as to have its spe- 
cific gravity so low as 7.816, then the most material part of the 
correction of 0.00017 is without foundation. 
A result nearly the same as that of Captain Kater and Mr 
Whitehurst, has been recently obtained at Greenwich by our 
celebrated astronomer-royal Mr Pond. His experiments were 
made with the apparatus which had been used in France, and 
which was left at the Royal Observatory by M. Arago in the 
summer of 1817.— -In our next Number, we expect to be able 
lo present our readers vdth an abstract of his results. 
