TEMPERATURE 151 



trating the mean surface temperature of the inshore zones, at 2-5 miles and 5-10 miles, 

 agree in showing a pronounced fall of temperature at Antofagasta and a recovery 

 which reaches its peak at Arica ; but within 2 miles of the coast water remains cool, 

 and this is interesting since there is no wind. After Arica, where the coast alters 

 direction and the winds had increased very considerably, the water within 5, 10 and 

 even 50 miles of. the shore was found to be cooler than it had been since the latitude of 

 Coquimbo. From San Juan to Callao another rise in temperature was taking place, and 

 this is where wind was blowing across the usual direction and towards the shore 

 (Fig. 4); the isotherms ran closer to the coast, the cooler water having disappeared 

 (Fig. 16). 



In the offshore zones, the curves for 10 20 miles, 20 50 miles, 50-100 miles and 

 100-200 miles, come under the influence of the warm-water wedge which is picked out 

 in Fig. 34 by heavy lines. Off Arica its influence is shown in the zones 10-20 miles and 

 20-50 miles, but lack of observations farther out makes its seaward boundary doubtful. 

 Off San Juan its influence is shown by the two outermost curves only. Off Callao, 

 where the warm-water wedge is close in, the curves for the io-20-mile and the 

 20-50-mile zones are affected and a big rise of temperature is shown, whereas at greater 

 distances from the coast the water is cooler. Northwards of Callao the wedge comes from 

 the open sea and a sharp drop occurs in the io-20-mile and in the 20-50-mile curves 

 and even in the 50-1 00-mile curve which continues to drop as it enters more northerly 

 latitudes. The N -shaped appearance of the warm-water wedge in this figure is of course 

 given by the arbitrary arrangement of the curves and by the latitude scale having been 

 compressed. 



I2°-5°S: GUANAPE ISLANDS, LOBOS ISLANDS AND PUNTA AGUJA 



In the month of July 8 to August 7, the ship made four traverses of this region ; once 

 to Salaverry and back to Callao, and once to the Ecuador coast and back : she was thus 

 able to make a more detailed examination of the current in this region than southwards 

 of Callao (Fig. 2). 



Northwards of Callao the spreading out tendency of surface isotherms is again in full 

 play and winds are consistently south east. It is most noticeable in the warm-water 

 wedge^ which first gains in width and then slants away from the coast to a distance of 

 over a hundred miles. In consequence, the lines of stations off the Guanape Islands, 

 Lobos Islands and Punta Aguja from 107 to 204 miles in length, all fail to span it 

 (Fig. 30). The shift seawards of the warm-water wedge has already been noted above 

 in the curves of mean temperature (Fig. 34). At the same time the wedge loses de- 

 finition. As it leaves the coast, the inshore waters become more and more homo- 

 geneous and the wedge less easily discerned. Whereas off Callao and the Guanape 

 Islands its inshore margin was distinguished by a sudden change of temperature, 

 farther to the north the surface temperature undergoes no sudden change (cf. the 

 gradual rise off the Lobos Islands and Punta Aguja, Fig. 30). This increasing homo- 



^ See footnote on p. 148. 



