276 Uiiiirrsitij of California Publicniions i)i Zoologtj [Vol. 15 



water. Imagine these processes of evaporation, absorption of solar 

 radiation, convection, and diffusion to take place during brief time- 

 intervals alternating with other intervals during which the entire 

 column of water is slightly elevated. Because of the relation of teni- 

 peratiire and salinity to depth in the region from Point Conception 

 to the Coronado Islands (see pp. 272 to 274). wliich ri'lation is sliown 

 diagrammatically by text-figures A and B (full lines), the elevation 

 of the entire column would result in a lower temperature at all levels, 

 a lower salinity at each level above that of its minimum value, and a 

 higher salinity at each level below that depth (text-figs. A and B, 

 dotted lines). During the next interval when the column of water 

 remained stationary the former processes of absorption, evaporation, 

 and diffusion would tend to produce the relations represented by the 

 full lines, and so on. 



The absorption of solar radiation which tends to heat the water is 

 accompanied by the processes of evaporation and convection which 

 tend to cool it. If these opposing influences are not balanced, the 

 temperatvire must change. For example, if the heat lost because of 

 evaporation and convection is less than that absorbed from solar radi- 

 ation the temperature will rise. But as it rises the rate of loss of heat 

 will increase ; and if the heat due to the absorption of solar radiation 

 is gained at a constant rate, the temperature will ultimately increase 

 until the heat lost equals that gained. 



Now, in order to deduce the effect of upwelling, let us suppose a 

 whole column of water is moved upward a small distance during a 

 brief time-interval, and that these processes of heating, evaporation, 

 etc., take place during the next interval, and so on. The temperature 

 in each part of the column will then be reduced during the intervals 

 when the column is moved upward, and raised during the other in- 

 tervals. But, in order that the temperature may rise during the 

 intervals of absorption, the actual temperature must be below the 

 normal. Therefore such a temperature will finally be reached that 

 its increase during the intervals of absorption will equal its decrease 

 during the intervals of upward motion; that is, a "steady state" will 

 arise in which the temperature is less than it would have been had 

 the column of water not been elevated. 



Similarly, the process of evaporation, which increases the salinity, 

 is accompanied by the opposing processes of convection and diffusion, 

 and if the rate of evaporation remains constant, a constant value of 

 the salinity will filially be reached. Imagine the above processes of 



