108 FOUNDEKS OF OCEANOGRAPHY 



and facilitating the hoisting in of the apparatus. He and 

 Captain Sigsbee together devised a new form of double-edged 

 dredge, generally known as the " Agassiz " or the " Blake " 

 dredge or trawl, which will work equally well whichever way 

 it falls on the bottom ; and also a very ingenious closing 

 tow-net (called the " gravitating trap "), which could be 

 lowered to any depth, opened and towed, and then closed 

 again, so that it was possible to strain the plankton or minute 

 organisms from a column of water of any given length at a 

 particular depth. As the result of experiments with this 

 apparatus, they were unable to find any planktonic organisms 

 in the region investigated below 100 fathoms from the 

 surface. These, and other later investigations with the 

 " Tanner " closing tow-net in the " Albatross," led Agassiz 

 to believe that, between the plankton fauna living at or near 

 the surface, say down to 200 fathoms, and that on or near the 

 bottom, there was a vast region where practically no life 

 existed. This theory (the non-existence of a mesoplankton), 

 with some modifications as to the extent of the upper zone of 

 life (he defined it later on, after experiments with the 

 *' Tanner " net in the " Albatross," as " a marked falHng off 

 below 200 fathoms "), Agassiz maintained to the end of his 

 days in opposition to most other oceanographers, including 

 his friend Sir John Murray. It was during the successive 

 voyages in the " Blake " that Agassiz was able to add to our 

 knowledge of that great warm current the Gulf Stream, 

 from the Strait of Florida to the Newfoundland Banks, and, 

 as the result of this and later work, to show the connection 

 between ocean currents and an abundant surface plankton 

 and the dependence of the bottom fauna upon the plankton. 

 It is interesting to note as the climax of Alexander Agassiz 's 

 connection with the Coast Survey that in 1885 President 

 Cleveland offered him the position of superintendent of the 

 whole of that work and Scientific Adviser to the Government. 

 However, considerations of health and of the probable 

 sacrifice of his own scientific work which would be necessary, 



