INTRODUCTION. XX J 



swollen, and the whole country is rendered impassable for a time. 

 These rains take place when the northerly monsoon returns charged 

 with the vapours from the tropics, which coming in contact with the 

 cooler atmosphere surrounding the highlands and mountains of Chili, 

 condensation takes place, and produces the violent rains during this 

 season. But, as this cannot take place on the northern coast and 

 its adjacent country, owing to the temperature not being low enough, 

 rain is rarely if ever experienced there. 



The variations which took place at the time of our visit will be 

 seen on the diagram before referred to. Our observations show a 

 barometric oscillation of '530, which appears to be about the extreme 

 range throughout the year ; its mean standing we found to be 29'896 

 inches. The temperature of the air varied from 65 to 46; mean 

 temperature 55'2. That part of Chili still inhabited by the Arau- 

 canians in the south, is said to possess a mild and equable climate : it 

 is considered the most fertile, having an abundance of everything, and 

 enjoying a happy mean between the extremes to which the other 

 parts are subject. Sun's radiation, by means of twenty-eight observa- 

 tions, was 68'4, shade 58'3, difference 1O1 ; greatest difference in 

 sun 39, the least 2. During our stay, the weather was for the most 

 part overcast both night and day ; the observations were taken when 

 it was clear. 



VALPARAISO TO CALLAo. In our passage from Valparaiso to 

 Callao, at about one hundred and twenty miles from the coast, we 

 passed beyond the influence of the northerly monsoons into the 

 southwest wind, and then into the trades, in latitude 28 30', which 

 is believed to be their southern limits at this season of the year. 

 On several successive days the wind veered even to the northeast 

 for a few hours; as we approached the coast of Peru, it became 

 more southerly and moderate. The temperature of the air increased 

 but 7 ; that of the water, only 5. It will be observed, by an inspec- 

 tion of the diagram on Plate VII., page 158, that when we were the 

 farthest from the coast, the temperature of the water rose several 

 degrees, proving satisfactorily that we were without the limits of the 

 Chili current, and that on nearing the coast of Peru we again 

 entered it. 



The mean height of the barometer had increased -087 in the 21 of 

 latitude. Although the sky was much overcast, we had no rain : the 

 degree of moisture was -949. 



CALLAO. It was the middle of the month of June when we 



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