Observations zvith Kater's Pendulums. 3 



The Shelton clock was suppofted by a couple of -|in. planks, 

 each of these being secured by large screws to four plugs inserted 

 about eight inches into the wall at the west end of the cellar. 

 The clock was attached to the planks by three screws, and set 

 vertically by inserting mahogany wedges between the planks and 

 the clock case. The verticality, as tested by the spirit level 

 attached to the clock, was well maintained during the whole 

 series of observations. 



The relative positions and tlistances of the apparatus wei'e 

 identical with those eui ployed in Melbourne,* save as regards 

 the position of the observing telescope (vide ififra p. 5). The 

 operation of inserting the pendulums into the cylinder was con- 

 siderably simplitied by cutting holes in the ceiling of the cellar, 

 and in the floor of the room above ; Mr. Russell would then hand 

 the pendulum down through the hole, I receiving it below and 

 guiding it into the cylinder ; in this way the pendulums, whnn 

 not lying in their boxes, were always kept in a vertical position 

 and supported by their upper ends, so that risk of accidental 

 bending was practically eliminated. The uppermost of the two 

 holes, when not in use, was kept closed by a board chamfered to 

 fit its edges, and above this again was a sheet of linoleum ; no 

 draught or air circulation through the holes was ever detected 

 during the swings. 



Pressure and Temperature. 



The experiments were carried on under atmospheric pressure, 

 tlie pressure being recorded by a marine barometer lent me by 

 Mr. Russell ; the cistern of the barometer was placed approxi- 

 mately on a level with the bob of the experimental pendulum. 

 The barometer corrections are given in Table I. 



» Baracclii, I.e., p. 1C4-6G. 



b2 



