194 University of California Publications. [Vol.6 



temperature under the pressure existing d fathoms below the 

 surface of the sea, we have, on substituting for p in the above 

 formula, its value in terms of the depth (d) : 



S d = S (1 + 7.9 X 10"" d) approximately. 

 If the temperature is the only variable, the following approxi- 

 mate formula holds between 10° and 30° Centigrade: 



S t = St [1 + (T — t ) ( .0002:. | ] 

 where St is the density at the temperature T and S t is the 

 density at the temperature t, using the Centigrade scale. So, in 

 order to find the actual density of the water under the conditions 

 existing in the sea, the value under standard conditions must be 

 corrected for both temperature and depth. More exact methods 

 for making these corrections are given in volumes I and II of 

 the Challenger report on Physics and Chemistry, and in Knud- 

 sen's hydrographie tallies. Publications />< Circonstance, No. II, 

 May, 1904. All densities given below are expressed in absolute 

 C. Gr. S. units and reduced to the standard temperature 15.56° ; 

 tin.' value used in the Chdlh ngi r report. 



PROPERTIES OF THE SURFACE WATER EXAMINED. 



In order to give a summary of this work, the day was divided 

 into eight periods of three hours each, the day beginning and 

 ending at midnight; the season was divided into periods of one 

 week each or one day, as seemed advisable, and the average 

 temperature was computed for each period. The number in 

 brackets represents the number of observations used to determine 

 the average. In case there were no observations for any given 

 period, the value was found by interpolation and inserted, so 

 that the weekly or hourly average would all depend on the same 

 number id' temperatures, distributed in the same way. 



It was found that certain in-shore and shallow water regions 

 had a temperature two or more degrees less than the rest of the 

 ocean, though there was no appreciable difference in the density. 

 The average weekly, hourly, and seasonal temperatures are com- 

 puted only from the warm water observations, which are much 

 more numerous and are representative of the normal surface 

 temperatures of the region. 



