NATURE OF THE STREAM 129 



A few years later. Professor Mitchell of the Coast and Geo- 

 detic Survey invented a system of deep weights and surface 

 floats joined by wires, with which he found that in the Straits 

 of Havana the current flows at full strength even at 400 fath- 

 oms. The work of many scientists, both from direct observa- 

 tion and from deduction, was later to show that not only the 

 main Stream runs deep, but that in many places enormous 

 volumes of water move in slow drifts far below the surface, in 

 directions quite different from those of the faster surface 

 currents. 



The most extensive single investigation of the Gulf Stream 

 ever to be carried out was begun in 1885 by John Elliot Pills- 

 bury, who anchored his vessel, the Blake, in various parts of 

 the Florida Straits. This in itself was a decided achievement 

 considering his limited equipment. Using special instruments 

 devised by himself, he spent two years measuring the currents 

 between Cat Cay and Miami, and actually stayed at anchor 

 in the middle of the Straits for a total of over 1,000 hours. The 

 instruments lowered into the water at each anchorage were 

 based on the simple device of rotating cups driven by the cur- 

 rent as an anemometer, or wind meter, operates, with a system 

 of gears attached to a revolution counter to indicate the rate 

 of flow. But anchoring in deep water puts a great strain on the 

 anchor cable and on the equipment. Moreover, the swinging 

 of the vessel about its anchor introduces such difficulties in 

 measuring currents that the method is not widely used in the 

 open sea, though it has considerable value and is very conven- 

 ient in shallow water. 



Pillsbury also measured the current off Cape Hatteras, at a 

 number of places in the Windward Islands passages, between 

 Cuba and Yucatan, and between Cuba and Key West. The 

 results were an unprecedented amount of entirely new data, 

 which added proof that part of the Equatorial Current side- 

 tracks the Caribbean Sea and flows northward outside the 



