Now it is probable that the main cause of oceanic circulation is the driving force of the winds upon the superficial layers of water; hence periodic and irregular changes in the direction and velocities of ocean currents are probably due to changes in atmospheric circulation traceable to changes in the quantities of heat absorbed from the sun by the earth's atmosphere.
In order to overcome the friction of the train the field-coils are wound with an auxiliary shunt coil which supplies a driving force sufficient to overcome the friction of the counting train.
Hence the disk will be accelerated until the driving force is balanced by the retarding force due to the induced currents created in the disk by the permanent magnets.
The driving force is balanced against a retarding force produced by the rotation of a copper disk fixed on the armature shaft, which rotates between the poles of a permanent magnet.
It is seen that the action is intermittent, liquid only being discharged during a down stroke, but since the driving force is that which is supplied to the piston rod, the lift is only con ditioned by the power available and by the strength of the pump. A continuous supply can be obtained by leading the delivery pipe into the base of an air chamber H, which is fitted with a discharge pipe J of such a diameter that the liquid cannot escape from it as fast as it is pumped in during a down stroke.
It ascends the flow pipe by convection, where its onward journey would speedily end if it were not for the driving force of other molecules of water following, and the suction set up by the gravitation into the boiler of the cooled water by the return pipe.
Since some ions are more mobile than others, a separation will ensue when water is placed in contact with a solution, the faster moving ion penetrating quicker into the water under the driving force of the osmotic pressure gradient.
The former was the driving force which made the First Crusade successful, where later Crusades, without its stimulus, for the most part failed; the latter was the one staunch ally which alone enabled Baldwin I.
Hence when a current is passed through the meter, the armature rotates and increases its speed until the driving force is balanced against the retarding force due to the eddy currents in the copper brake disk.
This main scheme is complicated in various ways: (r) by the rotation of the earth, which continually deflects currents of water or air to the right in the northern or to the left in the southern hemisphere; (2) by the conformation of the land masses (as in the case of the equatorial stream which is banked up in the Gulf of Mexico and flows out through the Straits of Florida); (3) by the varying depth of the ocean, for currents tend to flow more readily through deep than in shallow waters (as in the case of the main Atlantic drift, which flows most strongly through the deep channel between Shetland and the Faroe Is.); and (4) by the driving force of the winds acting on the surface of the sea (thus the drift of water from the equator is not N.E., as one might expect, but from E.