128 ANNUAL OF SCIENTIFIC DISCOVERY. 



of the land ; but the Caspian and Aral Seas, and the large lakes 

 of Asia, furnish proof of its former existence. By a simple 

 mechanical problem we can demonstrate why these ellipses were 

 formed. If near the edge of a disc rapidly revolving on its centre 

 a ball be placed, and caused by any means to pass alternately back 

 and forth on the radius, its motion will not be in a straight line, 

 but it will invariably traverse an ellipse. To make an applica- 

 tion : when the waters of the Gulf of Mexico have become heated 

 by the sun, the tendency will be to pass north until cooled, then 

 to return to the equator, and such would be the only motion were 

 the earth at rest ; but the revolution of the earth is a constant force 

 acting upon the current and gradually overcoming the northerly 

 motion, and turning it to the east, by the coast of Ireland. 

 Becoming cool, it seeks the warmer regions, and the easting is 

 transferred into a general southerly direction ; but, as it nears the 

 coast of Africa, its velocity is lost, and, as the earth moves more 

 rapidly than the current, the latter is left behind, or is giving an 

 apparent westward motion, till the Gulf of Mexico is again 

 reached, and the circle is completed. During the creation the 

 land appeared on the margin of, and between, the circles ; in 

 proof of which theory he advances the pointing of the three south- 

 ern continents to the south-east, first noticed by Huniboldt, 

 the accumulation of lands toward the north rather than the south, 

 and the direction of the glacial markings during the drift period. 



THE GULF STREAM. 



Henry Mitchell's observations indicate the depth of the Gulf 

 Stream to be scarcely more than one-third the maximum depth 

 of the channel. He concludes that the Gulf Stream is not a pro- 

 found movement, but an overflow of water from the gulf, having 

 for its office the restoration of surface level, while the office of the 

 counter-stream, or " polar current" beneath, is the restoration of 

 equilibrium thus disturbed between waters of different specific 

 weights or densities. This view of compensating currents is illus- 

 trated by observations in the Hudson River. In the dry season 

 (July) the surface outflow of the river through the Narrows has 

 been found to occupy three-fourths instead of half the 12 tidal 

 hours ; while in the under stratum the case is more than reversed, 

 and the inflow predominates to such an extent that, as a general 

 thing, it is constant along the bottom, although not in velocity ; 

 and the same conditions, with variable proportions, obtain for some 

 distance up the river. On running a line of levels from New 

 York to Albany, it was found that the bed of the Hudson River 

 lies below the mean level of the sea for over 100 miles, while the 

 surface of the fresh water, or river proper, in the dry season, is 

 above this level, yet not so much above as to counterbalance the 

 excess of specific gravity in the sea water, which consequently 

 during the summer months flows in along the bed of the stream, 

 while the fresh water overflows into the ocean. In other words, 

 the Hudson, for 100 miles, is in the summer but an arm of the sea 

 analogous to the Gulf of Mexico, deriving much of its elevation 



