224 



DEPARTMENT OF THE NAVAL SERVICE 



Let us now make a mental experiment. We imagine, in the centre of the area of 

 investigation, e.g., on Cape Breton island, a high tower, built in the form of a gasholder. 

 To the centre of the roof, on the inner side, is fastened a fine but strong cord, at the 

 lower end of which, reaching nearly to the floor, a heavy weight is attached, forming a 

 pendulum. This pendulum is set in motion, and the plane in which it moves marked 

 off by a line drawn on the floor at certain intervals of time. It will then be found 

 that the plane in question revolves in the same direction as the hands of a Avatch 

 placed with the dial upwards. The rate of progress is about 11° per hour; i.e., the 

 plane of the pendulum Avould make one complete revolution in thirty-three hours, 

 supposing that the pendulum itself could be kept in motion for that time. Fig. 2 

 shows the course traversed by the plane in the space of twenty-four hours. 



Fig-. 2. — The rotation of the pendulum 

 plane during 24 hours by a Foucault's 

 pendulum experiment on the New- 

 foundland area. 



The cause of this phenomenon is as follows : The plane in which the pendulum 

 oscillates does not, as a matter of fact, revolve at all ; what does revolve is Cape Breton 

 island and its surroundings, which turns with the earth's rotation about its axis. Sim- 

 ilarly, in our pendulum experiment, it is the tower which turns, at the rate of one 

 complete revolution in thirty-three hours, while the true plane of oscillation for the 

 l)endulum remains unchanged. The revolution of this plane is thus only apparent, 

 and, correctly interpreted, means simply that the whole of the Canadian Atlantic area 

 is rotating, at what, in consideration of its enormous extent, must be regarded as a 

 very high rate of speed. The direction of this rotary movement is counter-clockwise, 

 i.e., the reverse of the movement made by the hands of a watch dial upwards; the rate 

 of speed 



fa) ■ — ojo sm 



f' 



(1) 



where ip is the latitude, Wq the angular velocity of the earth about its axis, w the 

 angular velocity of the surface of the earth at a latitude amounting for the area in 

 question to about three-quarters of a revolution in the course of the twenty-four hours. 

 Fig. 3 shows the position of the Canadian Atlantic area at a moment of starting, 

 after 6 hours and after 12 hours. At the moment of starting, we have drawn in the 

 conventional manner ]^ upwards, S downwards, with E on the right and W to the left. 

 After the lapse of six hours, these points of the compass will have shifted 65°, and 

 after the lapse of 12 hours, 130°, to the left. The Gaspe and Cape North currents, 

 which in the first illustration are seen moving towards the right, continue their move- 

 ment in this direction, despite the rotation of the substratum, thus curving roimd 

 Gaspe and Gape Breton island, as shown in the two following diagrams. On the other 



