640 SEC. lo. 



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

 Captain Heaviside, K.E., in their pendulum operations in connexion with 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. 



The air pump served to exhaust the receiver, the vibrations being made 

 in a vacuum. 



The coincidences were observed by the small telescope erected at a 

 distance. 



3134. Pendulum Apparatus. Sabine. 



Kew Committee of the Royal Society, Kew Observatory. 



Pendulum vibration apparatus used by Sir E. Sabine, and similar to that 

 now in use by the Arctic Expedition under Captain Nares, R.N. 



It consists of a massive iron triangular frame, supporting a pair of agate 

 planes, upon which the invariable pendulum is swung ; a strong wooden 

 frame, carrying a Shelton clock, and a telescope, with which the coincidences 

 of beat of the detached pendulum and that of the clock are observed. 



3133. Photograph of a Reversion Pendulum Appa- 

 ratus, distance of knife-edges 1 metre from each other, executed 

 for the -Central Bureau of the European- Measurement of Degrees 

 at Berlin. A. Repsold and Sons, Hamburg. 



Pendulum Apparatus. The apparatus consists of the stand made of brass 

 tube, the pendulum, the scale, and the comparator. The pendulum is a brass 

 tube provided with knife edges. The scale is of the same tube as the pen- 

 dulum, and contains a steel tube, and this again a zinc tube, both of which 

 are united with each other and with the brass tube in such a manner that 

 for the determination of the temperature a small divided scale may be read off 

 near one of the end divisions of the main (brass) tube, which moves rela- 

 tively to the latter, by the different expansion of steel and zinc. The divided 

 surfaces are in the middle line of the tube. The scale may stand with either 

 end upwards. By rotation of the comparator round its foot-point the two 

 microscopes may be alternately directed upon the scale and upon the sus- 

 pended pendulum. 



3134a. Folding Alhidada or Sight- Vane, small size, for 

 hasty military surveys. M. Georges Sarasin, Genera. 



The plane table is plotted to scales of from ^^j. to ao ^ 00> so constructed as 

 to give, with an approximate exactitude which in no way hinders the rapidity of 

 the work (notwithstanding the small volume of the instrument for the sake of 

 portability), the measure of distances by means of a micrometer, and with the 

 optional assistance of an improvised sight, the measure of inclinations by 

 means of a clinometer furnished with a vernier permitting of readings being 

 taken to five minutes, and consequently the measure of the differences of 

 level, as well as a sketch of the horizontal lines on the ground, with the aid 

 of a calculating rule. It is possible to check any inaccuracies of centering by 

 verniers diametrically opposite to one another, and by turning the telescope 

 end for end. There are also means of regulation and correction. 



