214 PHILOSOPHICAL TRANSACTIONS. [anNO 1685. 



Peru runs along from the line southwards about lOOO leagues. It is said to be 

 divided into 3 parts, long and narrow, called Llanos, Sierras, and Andes ; the 

 Llanos or plains run along the South-sea coast ; the Sierras are all hills with 

 some valleys ; and the Andes are steep and craggy mountains. The Llanos are 

 about 10 leagues in breadth; the Sierras about 20 leagues, and the Andes the 

 same ; they run in length from north to south, and in breadth from east to 

 west. These parts of the world are said to have these things remarkable. 

 1 . All along the coast in the Llanos it blows continually with one only wind, 

 which is south and south-west, contrary to that which usually blows under the 

 torrid zone. 2. It never rains, thunders, snows nor hails in all this, coast, 

 though there falls sometimes a small dew. 3. On the Andes it rains almost 

 continually, though it be sometimes more clear than at other times. 4. In the 

 Sierras, which lie between both these extremes, it rains from September to 

 April, but in the other seasons it is more clear, which is when the sun is 

 farthest off, and the contrary when it is nearest. Now the reason of all seems 

 to be this : the eastern breezes which blow constantly under the line being 

 stopped in their course by the Sierras and Andes, and yet the same breezes 

 being to be found in the South-sea beyond Peru, as appears by the easy voyages 

 from Peru to the Philippines, a current of wind blows from the south on the 

 plains of Peru, to supply the eastern breeze in the South-sea ; and there being 

 but one constant gale in these plains, and no contrary winds, nor hills to beat 

 upon, this seems to be the reason why the vapours are never, or very seldom, 

 driven into rain. And the Andes being as high perhaps in many places as the 

 vapours ascend, in the highest degree of the atmosphere's gravity, this may 

 probably be the reason why the eastern breeze, beating constantly against these 

 hills, cause rains upon them at all seasons of the year. And the Sierras being 

 it seems lower than the Andes, therefore from September to April, when the 

 sun is nearest, and so the atmosphere's gravity less, and the vapours lower, they 

 are driven against the Sierras and form rain. 



The causes of those particular, various, uncertain and inconstant winds, 

 which blow without the tropics, and that most frequently in mountainous coun- 

 tries, and more seldom in great plains, such as Poland, cannot easily be con- 

 JQ^ctured : but those general winds, which usually take place every where about 

 the two equinoxes, seem to proceed from some general cause, and this I take 

 to be the change of the monsoons and trade winds, about these seasons, between 

 the tropics. For about these seasons, there must be a change of the balance 

 of the atmosphere, which must produce strong winds over all the earth. 



