262 G. F. McEwen. 



The difference between the actual temperature and the normal 

 temperature is due entirely to the mixture of cold water from the ad- 

 jacent ocean bottom with the surface water. 



The cold water upwelling in a particular region is due entirely to 

 the winds in that latitude, and no cold water from the surface in other 

 localities enters the region. 



Observations and deductions. An examination of the iso- 

 therms of Thorade's charts showed that the temperature of a surface 

 layer of water is approximately constant for a certain distance (x ) 

 out from the coast, and increases in proportion to the distance from 

 that point out to a point whose distance is (x 2 ) from the first, and re- 

 mains nearly constant from this point to the limit of his map, longi- 

 tude 140. Therefore the amount of heat in this layer of unit width 

 and thickness (y) would be 



where (T) is the actual in-shore temperature, and (to) is the normal 

 temperature for the latitude. 



Assume that this amount of heat is the same as if the total 

 volume y {x^ -j- x 2 + x 3 } was, to begin with at the normal temperature 

 (to.) and a volume (xy) at the temperature (to) was then removed from 

 the region and replaced by an equal volume (xy) upwelling from below 

 at the temperature (t ). (T) and (t 2 ) denote mean monthly temperatures 

 corresponding to the latitude, and(xy) will be assumed to be the volume 

 upwellling into the surface layer during the month's time ending with 

 the date to which (T) and (to) correspond. Equating the two expressions 

 for the amount of heat gives the equation 



12. y Xl T+-x 2 (T + to) + X3to = = ( Xl + x 2 + x s x) to + x 



The actual temperature at any instant is the result of the con- 

 tinuous action of various causes, absorb tion of heat from the sun, 

 radiation, evaporation and the intrusion of cold water. But, in order 

 to simplify the computation, it is assumed that the actual continuous 

 process can be replaced by the following artificial one. Assume that 

 whatever the temperature for any given month may be; the temper- 

 ature a month later would be normal were there no intrusion of cold 

 water; and assume that if all the water that actually intruded during 

 the previous month were then quickly mixed with the surface layer 

 the resulting temperature would be the same as the actual temperature. 

 A time interval of one month was adopted because the computation of 

 the mean temperature for each month can then be made directly, and 



