266 



E. F. PIGOT. 



fo.3 



have been made by himself. The lamp-circuit is capable 

 of being closed or opened at will, by a screw-switch placed 

 near the upper pole of the ball. The lens (plano-convex) is 

 stopped down to a very small aperture, and its focussing- 

 tube, when the pendulum is in position, can be easily 

 adjusted from the lower end of the supporting tube in 



which it slides. The 



sustaining wire is of 

 phosphor-bronze (diam. 

 1*5 mm.) attached above 

 to a specially construc- 

 ted knife-edge suspens- 

 ion of the Cardan type* 

 (fig. 4, and Plate XX, B), 

 permitting the pendulum 

 to continue oscillating 

 for many hours. This 

 Cardan suspension is 

 fixed on a stout beam 

 supported (as shown in 

 Fig. 3) on two heavy 

 steel girders at the top 

 of the main staircase 

 at Riverview College, — 

 a spot well suited for a Foucault-pendulum, and where I 

 had for many years contemplated erecting one, as sug- 

 gested to me as far back as 1891 by the late Father Charles 

 O'Connell, s.J. These girders are two out of a series, 

 about 1 metre apart, designed to support a very large water- 

 tank above the staircase. They measure 36 centimetres 

 vertically, and 14*5 centimetres horizontally at base. The 

 length of the whole pendulum is 13*7 metres, the ball hav- 

 ing a diameter of 18*5 centimetres, and weighing 27 kilo- 

 grams. The photographic paper is attached to a curved 

 platform, very rigidly fixed, the curved surface correspond- 



e 



General arrangement of experiment: 

 a, a, steel girders ; b, wooden beam, 

 rigidly wedged between girders; c, hole 

 for suspending wire; d, Cardan suspen- 

 sion ; f, platform for bromide-paper. 



