I 



NATURAL PHILOSOPHY. 179 



the time occupied in one pendulum gaining two seconds over the other. 

 The rate of one pendulum over the other is easily found; and as this opera- 

 tion is performed simultaneously at the upper and lower stations, nothing 

 remains but the comparison of the two clocks. In the Astronomer Roy- 

 al's former experiments in Cornwall, this was the most difficult part of 

 the operation. At that time it was necessary to fasten the chronometers 

 to the body by means of straps, and then to ascend or descend by perpen- 

 dicular ladders a journey which occupied considerably more than an hour 

 in its accomplishment. In the present experiments this section of the 

 observations is quite as satisfactory as, if not more than, the observation of 

 coincidences. This is owing to the adaptation of galvanism to astronomi- 

 cal purposes, and by this means the comparison of the clocks is effected. 

 A wire, properly coated with gutta-percha, passes from one pole of the 

 battery through a clock, which is so arranged as to push a spring, causing 

 a galvanic circuit every fifteen seconds. Erom the clock the wire passes 

 through a galvanometer attached to the clock-case at the upper station, 

 thence underground to the shaft, down which it descends to the lower 

 station, where it passes through another galvanometer, also attached to the 

 lower clock-case. It then returns up the shaft to the other pole of the 

 battery, and thus the circuit is completed. Signals were simultaneously 

 noticed by the observers at the upper and lower stations, which give a 

 direct comparison of the two clocks. 



FOUCAULT'S EXPERIMENTS. 



At the recent meeting of the British Association, M. Foucault, the vrell- 

 known author of the experiment for demonstrating the rotation of the 

 earth, and the inventor of the gyroscope, exhibited a series of experiments, 

 which are thus described in the record of the proceedings : 



The gyroscope is a massive ring of brass connected with a steel axis by 

 a thinner plate of the same metal, all turned beautifully smooth, and 

 most accurately centred and balanced ; in other words, the axis caused to 

 pass accurately through the centre of gravity, and to stand truly perpen- 

 dicular to the plane of rotation of the entire mass. On this axis was a 

 small but stout pinion, which served when the instrument was placed 

 firmly on a small frame, containing a train of stout clock-work, turned by 

 a handle like a jack, to give it an exceedingly rapid rotatory motion on its 

 axis. But to this clock-work frame it could be attached or detached from it 

 instantly. This revolving mass was only about three inches wide, and 

 four of them were mounted in frames a little differently. The first was 

 mounted in a ring, attached to a hollow sheath, which only permitted the 

 axle and the pinion to appear on the outside, so that it could be laid hold 

 of, or grasped firmly in the hand, if the pinion were not touched, while 

 the mass inside was rapidly revolving without disturbing that motion. 

 By this modification of the gyroscope, the author afforded to the audience 

 a sensible proof of the determination with which a revolving mass endeav- 

 ors to maintain its own axis of permanent stable rotation ; for upon setting 



