584 The Andes and the Amazons. 



this cold comes on. This cool change is also one of the 

 noted facts of the Lower Amazons as well, where the Por- 

 tug-uese know it as the tempo dafriagem (the time of cold) ; 

 and Bates, the English naturalist, who labored for many 

 years successfully on the Lower Amazons, thinks it to be 

 caused by a continuous cold wind blowing from the south 

 over the damp forests that extend from north of the equa- 

 tor to lat. 18° S., when it is winter in the southern hemi- 

 sphere ; and the cool currents of air traveling north to the 

 equator become only moderately heated in their course, 

 owing to the intermediate country being a vast, partially- 

 flooded plain, covered with humid forests. The warm 

 winds of this dry season are from the northwest, which 

 make the air very oppressive, though the great heat is only 

 for a short time, passing off in squalls, attended with thun- 

 der, liglitning, and light rain. In July, August, and Sep- 

 tember the variations in the thermometer are greatest; 

 and in these months is encountered the extreme range for 

 the year — from 19° to 29°. In these months, too, more 

 especially June and July, will be noticed fogs, which, how- 

 ever, disappear by 8 a.m. always, leaving the sky clear and 

 bright. Tlie average of annual heat for the whole Ama- 

 zons has been estimated at 26°. On the Maranon, proba- 

 bly it is some one or two degrees lower. This moderate 

 elevation of the thermometer for a tropical region enters 

 into the elements of present healthf ulness of this country. 

 Such is a brief outline of the topography and seasons of 

 the basin of the Maranon, or the Peruvian Amazons. With 

 such uniformity of temperature, and regularity of seasons, 

 if the two changes of the year may be so called, there is 

 in the diseases of this district a certain characteristic of 

 sameness also to be noted, the features of complaints being 

 distinctive, and not often varied. In the oi'der of fre- 

 quency the diseases may be mentioned as occurring thus : 



