72 



•cause experience now permits certain modifications in the program. 

 Twice during 1927, for example, we were able to gain a good idea of 

 the currents from a map based upon only 20 stations scattered net- 

 like over the region around the Tail of the Bank. The other three 

 surveys, however, dealt with a larger area situated along the eastern 

 slope of the Bank, and consequently they embrace more stations than 

 the earlier investigations. (See fig. 32, p. 70.) But the general plan 

 of sections placed at right angles to the currents underlies all of the 

 observational work. The choice of the particular area to be surveyed, 

 it should be remarked, is often dependent upon the relative position 

 of the ice and the patrol vessel, because we wish never to be far 

 distant from the southernmost bergs. 



A short description of the methods employed to determine the 

 currents is given herewith. First we decide on the ocean area in 

 which it is most desired to learn the direction and the velocity of the 

 circulation. Usually the waters between the United States-Europe 

 steamship tracks and the Tail of the Grand Bank are of first con- 

 sideration, because it is there the course of the cold current and its 

 freight of ice are subjected to the greatest variations in direction. 

 When respite from ice scouting occurs, the patrol ship cruises over 

 this zone; stopping and taking stations every 15 to 20 miles, the 

 points of observation being distributed equidistant over an area 

 which often approximates in size the State of Pennsylvania. 



A thoroughly drilled oceanographic team of four to six men starts 

 work when the vessel becomes stopped at the observation point. 

 As soon as the ship is "dead" in the water, a heavy weight attached 

 to a small wire rope is lowered over the side and an instrument called 

 a water bottle is securely clamped to the wire at the rail. The meter 

 wheel, which records the length of wire run out, is next set at zero, 

 the winch brake released, and the line allowed to unreel rapidly off the 

 drum. Six or seven water bottles are successively attached to the 

 wire at those levels at which we desire observations, until we reach 

 a depth of 750 meters, the limit to which the ice patrol has carried 

 the work. A water bottle, it should be explained, is an ingenious 

 mechanical instrument which, at the will of the observer, captures a 

 sample of the sea water in which it is immersed and simultaneously 

 registers the temperature by means of attached thermometers. 

 When all the water bottles are suspended on the wire at the proper 

 depths, a weight, called a messenger, is placed on the wire and, sliding 

 down, trips the first bottle. This causes the instrument to auto- 

 matically make a record and also release a second messenger which 

 in turn slides down to the second bottle, and so the operation is carried 

 on to the last bottle of the series. The wire is then reeled in, the 

 thermometers read, and the samples of the water from the respective 

 depths are bottled, the total elapsed time at a station being from 20 

 to 30 minutes. 



