1817.) Scientific Intelligence. 399 
served in the Ganges ; and Constantine has described it as occurring 
in the river of the Amazons. 
After a long continuance of dry weather, by which the waters of 
the Dordogne are very much reduced in quantity, we perceive at 
that part of its course where it mingles its waters with those of the 
Garronne this appearance presenting itself, asa huge mass of water 
somewhat resembling the form of a tun-barrel, which rolls from 
one side of the river tothe other, at one time disappearing, and at 
another rising again with increased dimensions and violence, and 
proceedivg up the river to the distance of about 22 miles. 
As soon as its approach is indicated, both men and cattle retire 
from its banks. 
From the suddenness of its appearance, and the violence with 
which it moves, it is often productive of serious evils. It has been 
frequently known to tear up by their roots trees which were growing 
on that side of the river to which it may have rolled, to sink or 
destroy boats, and to break down the banks of the river. 
The seafaring men who reside at the mouth of the river can 
generally predict the occurrence of the rat d’eau, from observing 
the depression in the river, and the force of the flowing tide. From 
these circumstances they are generally able to escape those unplea- 
sant and dangerous consequences to which this event gives rise. 
This remarkable phenomenon usually presents itself first opposite 
to the village of Bee d’Ambes. From this place it proceeds up the 
river, suffering a variety of changes in its appearance, till it reaches 
the town of Libourne, where it roars with apparently increased 
impetuosity, agitates the waters of the river to a considerable ex- 
tent, and at the same time suffers a very considerabie diminution in 
its size and in its force. 
This singular occurrence in the river Dordogne may doubtless be 
attributed to the combined operation of several causes, of which, 
however, the sea appears to be the most essential. 
At the flow of the tide its waters are conveyed by the Gironde to 
“the mouths of the rivers the Garronne and the Dordogne. Here the 
bed of the Garronne being considerably diverted out of the direction 
of the flowing tide, and the Dordogne being very favourably 
situated with regard to the Gironde, it (the Dordogne) receives a 
greater abundance of waters, which, entering with great rapidity, 
and penetrating very far in the form of immense waves, are thrown 
from side to side, and assume a variety of singular appearances. 
The diversified forms which the mascaret exhibits may be ascribed 
to the rapidity of the current of the river, to its numerous turnings, 
to the resistance which it meets from the sand-banks, and to a variety 
of other concurrent causes, 
Yours respectfully, 
Edinburgh, Nov. 15, 1816, TT. W. 
