THURAS: RECORDING SEA-WATER SALINITY 679 



stone bridge may, therefore, be considered as made up of ohmic 

 resistance, and only a single balance for resistance, as in a direct 

 current bridge, is necessary. 



The heating coefficient, i.e., temperature rise per watt dis- 

 sipated in the cell, for a stirred bath was found to be only 0.1 °C. 

 and did not change appreciably with the rate of 'stirring. In 

 an unstirred bath the coefficient was about 0.3°'C. For operating 

 the recorder about 0.05 ampere in the cell is needed. This 

 will raise the temperature of the sealed cell about one-fortieth 

 of a degree above the temperature of the bath and open cell. 



The differential temperature coefficient which is here ex- 

 pressed as the per cent change in the ratio of the resistances of 

 the two cells, containing different solutions, per degree change in 

 the temperature of the bath in which the two cells are immersed 

 was found at various temperatures. 



The following values of this coefficient were obtained for 

 salinities of 29 and 32 grams per 1000 in the two cells respectively. 



from to 10°— 0.00013 

 10 to 20°— 0.00009 

 20 to 30°— 0.00007 



From these values a small correction can be appHed if the 

 temperature of the sea water is different from the temperature 

 at which the calibration of the instrument is made. 



The thermal time constant of the cells, which is the time nec- 

 essary for the temperature of the cell to approach the tempera- 

 ture of the bath to 67 per cent of its initial difference in tempera- 

 ture, was found to be small. For a stirred bath the time con- 

 stant of the sealed cell is 37 seconds and the open cell 34 seconds, 

 and as in the case of the heating coefficient these values did 

 not change much with the rate of stirring. For an unstirred 

 bath the time constant was 62 seconds. As stated in the previ- 

 ous paper this small time constant is sufficient to bring the cells 

 quickly to the temperature of the bath for the maximum change 

 occurring in the temperature of the sea water. 



The effect of flow in the open cell was determined by passing 

 a thoroughly mixed solution through the cell from a large sup- 



