Astronomical and Nautical Collections, 105 



the same level of the sea ; and that at the equator its mean length 

 must be about 3901 inches. 



" The comparison of different methods of ascertaining the 

 length of the pendulum is highly important," says Captain Sabine, 

 page 37 1 ; " and by consequence the invention of new modes of 

 procedure. It is understood that a third method has been proposed 

 by Dr. Young, by means of a weight sliding on a rod, or bar, with 

 a single axis of suspension, as a yet more convenient method of ob- 

 taining a correct standard, than the processes of Borda and Kater. 

 It would be highly interesting to ascertain, by competent trial, the 

 relative values of the three methods, and to examine the corre- 

 spondence of their results ; or rather to work at them until they 

 should correspond, or until the reason of a difference should be 

 apparent." 



Without denying the justice of this conclusion, it may be re- 

 marked, that it is hardly fair either to Captain Kater, or to its in- 

 ventor, to call Dr. Young's lt a third method ;" because it was 

 suggested to the Committee of the Royal Society, and approved 

 by them, before the date of Captain Kater's very ingenious contri- 

 vance, and therefore before the demonstration of Laplace, which 

 showed that perfect sharpness was not necessary to perfect accu- 

 racy in the result of the convertible pendulum, and before that of 

 Dr. Young, which proved that the effect of a temporary compression 

 of the sharp edge would be inconsiderable, neither of which indis- 

 pensable circumstances were foreseen by any person at the time 

 that Dr. Young thought his more complicated arrangement neces- 

 sary ; any more than it could be foreseen with what admirable deli- 

 cacy of experiment, or with what persevering iudustry, Captain 

 Kater would overcome the difficulty of making his measurement 

 from one of two opposite sharp edges to another, instead of the 

 much more convenient process of reading off by a micrometer the 

 distances of the fine lines only, which were to be drawn on the rod 

 of Dr. Young's pendulum. 



It is indeed doubtful whether any future experimentor would be 

 likely to obtain a result so nearly agreeing with Captain Kater's, by 

 his own method, as by that of the sliding weight, in which so little 



