

A PHOTOGRAPHIC FOUCAULT-PENDULUM. 



265 



"To carry the cutting tool, one end of an L-shaped lever was 

 bolted and pivotted to the bed of the lathe centrally beneath the 

 equator of the ball, the other end carrying the cutting tool at the 

 exact height necessary to sweep out a meridian accurately from 

 the poles. With the ball slowly revolving, this tool was used 

 until the rough surface was removed, and the ball became an 

 approximately true sphere. The final shaping was given by the 

 use of a piece of five inch diameter tube, having the end ground 

 sharp, pressed against the revolving ball until the edge was in 

 contact with the ball surface at all points, and in all positions. A 

 template cut out of flat brass to the exact radius was used to 

 verify the work from time to time. 



"With the accumulators 

 and central tube in position, 

 the geometrical centre of the 

 ball was determined, and a 

 disc with a conical depress- 

 ion in its centre, was fixed 

 at this point in the tube. 

 A long steel rod fixed to a 

 pedestal and pointed at the 

 top was introduced into the 

 tube, and the ball was bal- 

 anced on this point, holes 

 being drilled in the heaviest 

 sides, from the interior, until 

 the ball hung on the point 



Plan of Pendulum-bob (through 

 equator). 



without tendency to tilt or rock in any way." 1 



The ball and its contents, as well as the knife-edge 

 suspension for the whole pendulum, have been carefully 

 prepared under Mr. Murday's supervision, and some of the 

 more delicate electrical connections for the glow-lamp 



1 As an additional precaution, with the kind assistance of Professor 

 Von wilier, the ball was floated in a basin of mercury, at the Physics 

 Laboratory, University of Sydney, and further trimmed till equilibrium 

 was obtained. 



