R(q>oi't on the. Gnwilf/ Survey of AustniUma. 221 



A tap attached to the side of the cylinder is connected by 

 rubber tubing to a Siphon barometer, and a second tap 

 allows of the attaclinient of an air-pump in order to reduce 

 the pressure to any desired amount, wliich is measured on 

 the Siphon barometer. 



As the tail-piece is only a little way above the ground, 

 the short telescoj)e with diagonal eye-piece sent with the 

 apparatus is highly inconvenient. It is proposed to view 

 the coincidences by means of a long telescope of considerable 

 aperture, iuclined at a small angle to the ground, and 

 carrying a plane mirror in front of the object glass, so as 

 to reflect the image of the apparatus in a nearly vertical 

 direction. This method will result in a considerable saving 

 of light, and a much m(»re than considerable addition to the 

 comfort of the observei-. Anyone who has had experience 

 in really delicate })hysical work will understand the 

 importance of these considerations to the accurac}'^ of the 

 experiments. 



In order that the images of the detached and ch^ck 

 j)endulums may be in the same plane, a large lens is 

 provided, by means of which an image of the clock 

 pendulum is thrown on the ground glass scale inside the 

 cylinder. The lens is mounted on a brass angle piece, 

 which slides on a brass frame attached to a wooden stand. 

 The stand rests by means of three levelling screws on a 

 ]»lank bolted to the framework which supports the cylinder. 



