£p EXPERIMENTS ON CURRENTS. 



stream of the tide: but the barge, without any assistance 

 of oars or towing, passed on, overtaking the stream, as;d her 

 boat was towing astern. I fastened a riband to the end 

 of a stick, and immersed it in the water about 20 inches, 

 which was as low as the lowest part of the barge's bottom, 

 and therefore sufficient to have shown, by the direction of 

 the streamer, if the barge had been impelled forward by 

 superior velocity of the under current, as in that case the 

 streamer would have gone before the stick ; but the 

 streamer tended towards the stern, and was drawn after the 

 stick : whence it was evident, that the barge's progress ex- 

 ceeded that of the stream underneath as well as on the sur- 

 face, and that this excess was acceleration produced by some 

 other cause*. 

 The surface of As by the general law of gravitation the heaviest bodies 



a stream an m- descend with most velocity in a yielding medium, so it an- 

 chned plane. .... 



pears to be with bodies floating in a stream. The surface 



of a stream or current of water is not horizontal, but an 



inclined plane, and the inclination of the surface produces 



the current. Thus, when, by the attraction of the Sun or 



Moon, the sea is raised in some parts, it becomes depressed 



in others, and the water, seeking to regain its level, flows in 



a current from the superior parts. 



The barges on the river in a calm therefore slide doicn- 



ward with the stream, and also on it. 



Wherry out- A friend of mine in a wherry going to pass under Lon- 



stnpped by a ^ on bridge, being closely preceded by a coal barge, was 



apprehensive of receiving damage from collision with the 



barge when under the bridge; but the waterman said the 



barge would shoot far enough ahead when she came to the 



indraught of the arch. And it happened accordingly ; for 



Under currents * No part of what is here said contradicts any received hypothesis 

 produced by concerning under currents. Some under currents proceed from visible 

 ' causes, as when the wind blows for a length of time in one direction 



towards a coast, especially if it is an embayed coast, whereby the wa- 

 ters are accumulated and the surface near the shore is raised above the 

 general level, till the pressure of the increased weight forces back the 

 water underneath. Under currents, where the causes ace not visible, 

 may be supposed to be caused by inequalities in the bottom, in the 

 same manner as eddies are caused by the projecting points of a coast 

 interrupting the general course of a stream, 



the 



