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XIV. On the Discoi-dancies in the Results of the Methods for 

 deterrniiiing the Length of the simj)le Pendulum. By Francis 

 Baily, Esg. F.E.S. S-c. cfc. ^c* 



TT is well known to many persons that I have, for some tune 

 ■*■ past, been engaged in making experiments on the converti- 

 ble pendulum, with a view to satisfy myself of the accuracy of 

 the generally received determination of the length of the sim- 

 ple pendulum, vibi'ating seconds, in this latitude. The result 

 of those experiments has convinced me that we are, at prese?iff 

 very far from possessing in that instrument a method of de- 

 ducing a standard measure. The pendulum employed was 

 one similar to that which has been already described in the 

 Phil. Mag. for August last, page 137; and is in fact nothing 

 more than a plain straight bar of brass, about 62 inches long, 

 2 inches wide, and f of an inch thick; without any moveable 

 weights or sliding pieces : and the knife edges are so placed 

 that the vibrations made on them are synchronous with each 

 other. The distance between the knife edges (the determina- 

 tion of which is by far the most troublesome and difficult part 

 of the process) has been determined from a mean of nearly 

 one hundred comparisons with Sir George Shuckburgh's 

 standard scale; which was kindly entrusted to me for that pur- 

 pose, by the Council of the Royal Society, who now possess 

 that invaluable instrument. This distance is S9"3069 inches: 

 and the number of synchronous vibrations made on the knife 

 edges, in a mean solar day, corrected for the arc, for the tem- 

 perature, for the reduction to a vacuum, and for the rate of 

 the clock, is 86208*70 : consequently, the length of the simple 

 pendulum will be 



("^S?")^^ 39-3069 = 39-1330 inches. 

 But, Captain Kater makes the length of the simple pendulum 

 (reduced to the level of the sea) e(|ual to 39-13929 inches. If 

 we strike off the last two figures, for the amount of the correc- 

 tion for reducing it to the level of the sea, we shall have, in 

 round numbers, 39*139 inches as the value of Captain Kater's 

 measure, determined near the same spot as my own : and it 

 will be unnecessiiry to carry our inquiries into the value of 

 the fourth figure in the decimal, when we disagree so much 

 in the value of the third figure. 



Knowing the accuracy with which Captain Kater's experi- 

 ments were conducted, and having minutely examined every 

 step of the process detailed by him in his excellent paper on 



* Cominunicatcd by tlie Autlior. 

 Nfxo Series. Vol f}. 'No. 2G. Feb. IH'29. O the 



