WEIBEL AND THURAS: RECORDING SALINITY 149 



practical considerations, it was necessary to increase the diam- 

 eter in order to reduce this coefficient. 



To determine the temperature lag, different cells were placed 

 in a stirred bath and their time constants were found by chang- 

 ing their temperatures slightly from the temperature of the bath 

 and reading the resistance at definite intervals as the cell gradu- 

 ally assumed the temperature of the bath. By time constant 

 is here meant the time necessary for the temperature of the cell 

 to approach the temperature of the bath to 67 per cent of its 

 initial difference in temperature. 



The time constants were found to be very approximately 

 inversely proportional to the square of the diameter of the cells. 

 Therefore the condition that is required to reduce the heating 

 coefficient is opposite to that which will reduce the time constant, 

 and since both of these values must be small special multiple tube 

 cells were designed which will fulfill these conditions. 



The time lag produced by a change in concentration of the 

 sea water was determined by passing water of different salinities 

 through a cell and it was found that if the cell is being swept out 

 at the rate of three or four volumes a minute the ratio will re- 

 spond within three or four minutes for probably the maximum 

 change in salinity which can occur. The following considera- 

 tions will show the purpose of reducing these factors as much as 

 possible. 



In general the temperature and salinity of the ocean changes 

 very gradually from place to place so that usually no special 

 cell would be required to record the salinity, but at some places 

 as for instance in the vicinity of the Grand Bank of Newfound- 

 land, where the cold fresh water of the Labrador Current meets 

 the warm salty water of the Gulf Stream, the temperature and 

 salinity change comparatively rapidly in moving from one body 

 of water to the other. At these places such a specially designed 

 cell is necessary. A few years ago a number of temperature 

 records of the ocean were taken from a vessel going at moderate 

 speeds and the most sudden change in temperature was 3.5° in 

 about one minute. If this change is assumed to be instantane- 

 ous, the temperature of the sealed cell will in less than two min- 



