Wilhems Plains.] 
TERRA AUSTRALIS. 
423 
The district or quarter called Wilhems Plains, occupies a con- 
siderable portion of the interior of the island ; its northern extremity 
borders on the sea by the side of the district of Port Louis, from 
which it is separated by the Grande Riviere ; and it extends south- 
ward from thence, rising gradually in elevation and increasing in 
breadth. The body of the quarter is bounded to the N. E. by the 
district ol Mocha, — to the S. Eh by that of Port Bourbon or the 
Grand Port, — to the south by the quarter of La Savanne, — tyid to 
the west by the Plains of St. Pierre. Its length from the sea to the 
Grand Bassin at its southern extremity, is about five geographic 
leagues in a straight line, and mean breadth nearly two leagues; 
whence the superficial extent of this district should not be much less 
than ninety square miles. In the upper part is a lake called the 
Mare aux Vacouas, apparently so named from the number of pan- 
danus trees, called vacouas, on its borders; and that part of Wilhems 
Plains by which the lake is surrounded, at the distance of a league, 
more or less, bears the appellation of Vacouas ; in this part my 
residence was situate, in a country qverspread with thick woods, a. 
few plantations excepted, which had been mostly cleared within a 
few years. 
In consequence of the elevation of Vacouas, the climate is as 
much different from that of the low parts of the island as if it were 
several degrees without the tropic ; June, July, and August are the 
driest months at Port Louis, but here they are most rainy, and the 
thermometer stands from 7 0 to iq° lower upon an average through- 
out the year.* In a west direction, across that part of the Plains 
of St. Pierre called Le Tamarin, the sea is not more distant 
* The mean height of the thermometer in July 1805, which is the middle of winter, 
was 671°, and of the barometer in French inches and lines, 26,71; and during February 
1806, the middle of summer, 76° and 26.5 f were the mean heights. At M. Pitot’s house 
in the town of Port Louis, the averages in the same February were 86 ° and 27.7-f . Ac- 
cording to De Luc, the difference between the logarithms of the two heights of the baro- 
meter expresses very nearly the difference of elevation in thousand toises, when the thcr- 
1805. 
September. 
