Observatiojis ivith Kater's Pendulums. 15 



metrical Survey. I cannot discover any record of experiments 

 directed to discover whether the vibrations of the pendulums set 

 up any corresponding^ vibration in the cylinder. It appeared 

 desirable to investigate the question ; and Mr. Eussell very 

 kindly constructed the apparatus here described, and assisted in 

 the conduct of the experiments made with it. 



The apparatus is figured in Plate 1. ABD, Fig. (1),* is an 

 L-shaped biuss plate, to whicli two small plates J/, M, Figs. (1) 

 and (2), are soldered above and below. Through the plates M, 

 M, screws T, T, Fig. (2), are passed, terminating in conical 

 pivots which work easily in sockets in the brass plate EF ; G, 

 Fig. (1), is a weak spring fastened to EF, and bearing against 

 the arm AB of the L-shaped piece, so that when left to itself 

 the arm BD is pi-essed into contact with EF ; to the arm BD 

 a mirror, C, is cemented; F, Figs. (1) and (2), is a conical steel 

 spike. The plate EF is secured by three screws to the wooden 

 block K, which is itself screwed to the top of a large iron drum, 

 ZT, filled with water, which stands on the fiuor. When in use 

 the point of the .spike F rested perpendicularly against the north 

 window of the cylinder, against which it pressed with sufficient 

 force to bring the arm BF) parallel to the plate EF ; it was 

 found that a force equal to the weight of 0-25 ounces was 

 required for this purpose. The plane of the thrust is parallel to 

 the plane of vibration of the pendulum. 



At the other end of the cellar a frame carrying a telescope and 

 scale was supported by means of a similar iron drum filled with 

 water, to which it was screwed, in such a way that an image of 

 the scale was thrown into the telescope by the mirror ; the 

 telescope was provided with a single vertical crosswire. The 

 arrangement of the telescope and scale is shown in Figs. (3), (4) 

 and (5), and needs no further explanation. The scale was divided 

 on ground glass into inches and tenths, and illuminated by a 

 small bull's-eye lantern placed behind it on the frame. A 

 displacement of one-tenth of a scale division in the image would 

 have been easily detected, especially if oscillatory. 



The dimensions of the apparatus were as follows : — Distance 

 from point of spike F to vertical line of pivots, 0'75 in. Distance 



* Fig. (1) is liorizoiital, Fig. (2) is vertical. 



