438 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1956 



they will drift just clear of bottom obstructions and be carried by 

 bottom currents. 



RED TIDE 



This is one of several hundred cards released along the West Coast of Florida for 

 the study of currents in connection with the Red Tide. Your cooperation in giving 

 accurate information and returning the postage-free card will be greatly appreciated, 

 and will be very beneficial to you and your neighbors. 



Date and Time found m. 



Where found 



(Name of Beach, Key, Place on shore, near what city, or other prominent reference 

 point. OR, if at sea, exact latitude and longitude.) 



Name and Address of Finder 



The back of a prepaid postal card used in drift bottles and in pliofilm envelopes 

 for investigating currents in their relation to Red Tide 



DRIFT CARDS 



An interesting variation in the use of drifting floats is the drift card, 

 which consists of the usual information postal card enclosed in a 

 transparent pliofilm envelope so that it floats. During investigations 

 of the Florida Red Tide, The Marine Laboratory of the University 

 of Miami used thousands of these cards. They were distributed from 

 a fleet of private motorboats in such a way that very large areas of 

 water were covered, and when picked up by the same fleet some 

 days later an unusually detailed picture of the complicated system of 

 currents and eddies off the west coast of Florida was obtained. 



The interpretation of float records is full of difficulties, since any 

 one bottle, card, or float can only tell the beginning and end of its 

 course and the time taken. It does not show whether the course was 

 direct or indirect. An example of this was given by Dr. Tait in his 

 study of the North Sea currents in relation to fisheries. Bottles 

 released at one place were picked up near the coast of Jutland at 

 various times. The times taken for them to reach the place where 

 they were picked up were in multiples of 20 days. The explanation 

 was that there is a big eddy off the Jutland coast and that the circula- 

 tion time of the eddy is about 20 days. Some bottles completed the 

 course once, but others went around twice or even more before being 

 picked up. 



RADIO FLOATS 



As electronic devices are being applied more and more to oceano- 

 graphic problems and instruments today, it is not surprising to find 

 the drift buoy or float undergoing its own kind of evolution. Floating 



