VOL. XV.] PHILOSOPHICAL TRANSACTIONS. ^13 



in our winter season, when the sun is in the southern signs ; and their southern 

 ones in our summer, when he is in the northern signs. 



The rivers Indus and Ganges, where they enter the ocean, contain between 

 them a large peninsula, which is divided in the middle by a ridge of high hills, 

 called the Gatae, which run along from east to west, and quite through to 

 Cape Comorin. On the one side is Malabar, and on the other Coromandel. 

 On the Malabar side, between that ridge of mountains and the sea, it is what 

 they call summer from September till April ; in which time it is always a clear 

 sky, with little or no rain. On the other side the hills, on the coast of Coro- 

 mandel, it is at the same time their winter, every day and night yielding abun- 

 dance of rain ; and from April to September it is on the Malabar side their win- 

 ter, but on the other side their summer ; so that in little more than 20 leagues 

 journey in some places, as where they cross the hills to St. Thomas, on the one 

 side of the hill you ascend with a fair summer, on the other you descend with 

 a stormy winter. The like is said to obtain at Cape Razalgate in Arabia. And 

 Dr. Trapham relates the same of Jamaica, intimating that there is a ridge of 

 hills running from east to west through the middle of the island, and that the 

 plantations on the south side of these hills have from November to April a con- 

 tinual summer, whilst those on the north side, have as constant a winter, and 

 on the contrary from April to November. 



From these and such like accounts, it seems evident that a bare diminishing 

 of the atmosphere's gravity will not cause rain, but that there is also requisite 

 either a sudden change of winds, or a ridge of hills to meet the current of the 

 air and vapours, whereby the particles of the vapours may be driven together, 

 and so fall down in rain. And hence it happens, that whilst the wind blows 

 from the north-east, viz. from November to April, there are continual rains in 

 the northerly plantations of Jamaica, and on the side of Coromandel in the 

 East Indies ; because the winds beat against that side of the hills : and so there 

 is fair weather on the other side, there being no winds to drive the vapours to- 

 gether. But in the southerly monsoon, viz. from April to November, Malabar 

 and the southern plantations of Jamaica have floods of rain, the wind beating 

 against that side of the hills ; whilst in Coromandel and the other side of Ja- 

 maica there is fair and clear weather. The maps make those mountains of 

 GataB run south and north ; and if so, the monsoons must blow from other 

 points, by reason of the neighbouring countries and islands, or else this is not 

 the true cause of these seasons. 



This serves also to clear up the singularity of seasons in Peru beyond any 

 other parts of the earth, and seems to be assigned by Acosta as the cause of it 



