738 SEC. 15. GEOGRAPHY. 



3025. Water Bottle. Buchanan's ; date 1872. A drawing. 

 Invented by Mr. Buchanan, one of the scientific civilian staff 

 attached to " Challenger." 



3026. Barometer, Diagonal (about 1750). Watkins and 

 Smith, London. 



302 6a. Barometer with Thermometer. 



Paul Greiner, Hamburg. 



The baro-thermometer, an instrument for measuring the depth of the sea, 

 is also intended for recording the temperatures and the salinity of the sea 

 water. 



III. SURVEYING AND OTHER INSTRUMENTS LENT 

 BY VAEIOUS CONTRIBUTORS. 



3026b. Kater's Reversible Pendulum. 



The Royal Society. 



The original pendulum employed by Kater (Phil. Trans, for 1818), with 

 the tail-pieces subsequently modified by Sir Edward Sabine (Phil. Trans, for 

 1829). 



The pendulum is made to vibrate with one of the steel wedges called 

 " knife-edges," resting on firmly-supported and carefully-levelled agate planes, 

 and the vibrations are referred to a clock by the method of coincidences. 

 The pendulum is then inverted so as to vibrate about the other knife-edge, 

 and the movable weights are adjusted by a combination of calculation and 

 trial, till the times of vibration about the two knife-edges are found to be the 

 same. In this condition the length of a simple pendulum vibrating in the 

 same time as the Kater is equal to the distance between the knife-edges, 

 which Can be accurately measured ; and the length of the seconds pendulum 

 will then be got by dividing by the square of the time of vibration expressed 

 in seconds. 



This pendulum has just been employed in a re-determination of the length 

 of the seconds pendulum, particulars of which are nearly ready for publi- 

 cation. 



3132. Pendulum Apparatus. Great Trigonometrical Sur- 

 vey of India. Kew Committee of the Royal Society. 



The pendulum vibration apparatus used by Captain Basevi, R.E., and 

 Captain HeaViside, R.E., in their pendulum operations in connexion w.ith the 

 Great Trigonometrical Survey of India, 1865 to 1874. 



It consists of a vacuum chamber, of stout copper, firmly supported by a 

 strong wooden stand ; the chamber contains in its upper part a pair of agate 

 plates, upon which the knife edge of the pendulum rests, and it has at, the 

 bottom an apparatus for starting and stopping the pendulum, as well as a 

 graduated arc for determining its extent of motion. In the chamber there is 

 also a fixed pendulum containing thermometers. 



The Shelton clock exhibited with the other pendulum apparatus was used 

 for timing the vibrations of one pendulum in the receiver, being firmly fixed 

 to a wall erected for the purpose behind it. 



