new standards of weights and measures, 51' 



POSTSCRIPT. 



Since the preceding Paper was read, I have received a 

 work on Astronomy, published at Tubingen in 18 n, by 

 Professor Bohnenberger. This work had been pointed out 

 to me by Professor Schumacher as containing a description 

 of the convertible pendulum, and a suggestion of its employ- 

 ment for the purpose of determining the distance between 

 the centres of suspension and oscillation. 



A friend has favoured me with a translation of the part irt 

 question, by which I find M. Schumacher's information to 

 be perfectly correct, and that the conception of the converti- 

 ble pendulum is not so new as I had imagined when I first 

 engaged in this enquiry. After demonstrating the recipro- 

 city of the centres of suspension and oscillation, the author 

 proceeds to say : ** On a cylindrical or prismatic rod C A 

 " (fig. 102.) let there be placed two wedge-formed axes 

 ** at C and c, whose edges being turned towards each other, 

 " are perpendicular to the rod and parallel to each other. 

 " Let the one be at the end C of the rod, and the other at c, 

 " distant from C something more than two-thirds the length 

 " of the rod, so that the centre of oscillation 0, about the 

 " edge C, may fall between C and c. On the remaining 

 " part, cA of the rod, let a small weight n, slide backwards 

 " and forwards. Now, by a diminution of the mass of the 

 ** rod on one or on the other side, it is easy to manage, that 

 " if this pendulum be suspended on its edge C, a plumb line 

 " hanging down from this, falls upon the edge c, conse- 

 " quently the centre of gravity of the pendulum falls in the 

 ** plane of the axis of rotation. By sliding the weight n, the 



