and bones in a fossil state, creates a considerable degree of surprise ; 

 and by connecting the present animals with those that are extinct, 

 adds a link to that chain of gradation which is the most interesting 

 to the comparative anatomist and to the geologist. 



An Account of Experiments for determining the Length of the Pendu- 

 lum vibrating Seconds in the Latitude of London. By Capt. Henry 

 Kater, F.R.8. Read January 29, 1818. [Phil. Trans. 1818, 

 p. 33.] 



It has long been a desideratum in science, to determine the pre- 

 cise length of a pendulum vibrating seconds in a given latitude. 

 Most of those who have undertaken this inquiry have endeavoured 

 to find the centre of oscillation ; but as this depends upon the regu- 

 lar figure and uniform density of the body employed, it involves 

 difficulties which may be considered as insurmountable. Despairing, 

 therefore, of success in any attempt founded upon such principle, 

 Captain Kater endeavoured to discover some other property of the 

 pendulum less liable to objections ; and was so fortunate as to per- 

 ceive one which promised an unexceptionable result. 



It is known that the centres of suspension and oscillation are re- 

 ciprocal ; or, in other words, if a body be suspended by its centre of 

 oscillation, its former point of suspension then becomes the centre of 

 oscillation, and the vibrations in both positions will be performed in 

 equal times. Now as the distance of the centre of oscillation from 

 the point of suspension depends upon the figure of the body em- 

 ployed, if the arrangement of its particles be changed, the place of 

 the centre of oscillation will also suffer a change. Suppose, then, a 

 body to be furnished with a point of suspension, and another point 

 on which it may vibrate, to be fixed as nearly as can be estimated in 

 the centre of oscillation, and in a line with the point of suspension 

 and centre of gravity ; if the vibrations in each position should not 

 be equal in equal times, they may readily be made so, by shifting a 

 moveable weight, with which the body is to be furnished, in a line 

 between the centres of suspension and oscillation ; when the distance 

 between the two points about which the vibrations were performed, 

 the length of a simple pendulum, and the time of its vibrations, will 

 at once be known, uninfluenced by any irregularity of density or of 

 figure. The mode of suspension which the author adopted was the 

 knife-edge, of which the various advantages and disadvantages are 

 pointed out, and the modes of overcoming the latter described. 



The pendulum consisted of a thin bar of plate-brass, pierced with 

 two triangular holes at the distance of 39'4 inches from each other ; 

 to admit the knife-edges, which were made of wootz, and finished to 

 an angle of 120, and firmly screwed to brass knee-pieces. The 

 pendulum is prolonged at either extremity by a slip of deal, extend- 

 ing about twenty-two inches beyond the knife-edges. Three weights 

 are employed for the adjustments. The great weight is immoveably 

 fixed beyond the knife-edges ; the second weight slides on the bar, 



G2 



