S U M A T R A, ig 
tbftt bearing nearly in its whole extent, and accordingly coincides with 
the direction of the S, E. monfoon, when that prevails. Whilfh the 
fun is near the line, the winds are variable, nor is their dirc^ioa fixed 
till he has advanced feveral degrees towards the tropic ; and this is the 
caufe chat the monfoons ixfually fet in, as I have obierved, about May 
and November^ inftcad of the equinoSial months. 
Thus much is fufficient with regard to the periodical winds. I fliall 
proceed to give an account of thofe diftinguiflied by the appeliation of 
land and fea breezes, which require from me a minuter invetHgation, g^^^^^^J^*^ 
both bccaufe, as being more local, they more particularly belong to 
my fubjedt, and that their nature has hitherto been lefs accurately treated 
of by naturalifts. 
In this iHand, as well as ail other countries between the tropics, of 
any confiderable extent, the wind uniformly blows from the fea to the 
land, for a certain number of hours in the four and twenty, and then 
changes, and blows for about as many from the land to the fea : except- 
ing only when the monfoon rages with remarkable violence, and even at 
fuch time the wind rarely fails to incline a few points, in compliance with 
the efforts of the fubordinate caufe, which has not power, under thofe cir- 
cumftances, to produce an entire change. On the weft coaft of Suma- 
tra, the fea breeze ufually fets in ; after an hour or two of calm ; about 
ten in the forenoon, and continues till near fix In the evening. About 
feven, the land X^r^^f- rnmcs off, and prevails through the night, till 
towards eight in the morning, when it gradually dies away, 
Thefe depend upon the fame general principle that canfes and regu- cwre of the 
lates all other wind. Heat ading upon air rarefies it, by which it be- Biteter^ 
comes fpccifically lighter, and mounts upward. The denfer parts of 
the atmofphere, which furround that fo rarefied, rulh into the vacuity 
from their fuperior weight ; endeavouring, as the laws of gravity re- 
quire, to reft ore the equilibrium. Thus in the round buU dings where 
the manufactory of glafs is carried ooj the heat of the furnace in the 
center 
