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from the 7th September to the end of October; in 1815 from the
5th to the end of August; in 1819 from the 14th August to the end
of that month; in 1824 from 21st June to the end of September; in
1825 it was above water from the 9th to the 23rd of September;
and in 1826 from the 11th July to the end of September: the
uncommon circumstance of its appearing in three successive years
may be attributed to the extraordinary warmth of the seasons. It
rose above water again on the 10th June 1831 and remained
uncovered till the 19th July.
It would be tedious to investigate every hypothesis which has
from time to time been put forth to account for this phenomenon -
with the arguments for and against each - some assuming water,
others air, as the chief agent in its production.
A small mountain stream which pours down a rock opposite the
place, and runs underground before it reaches the lake, has been
employed in various ways to account for its rising; and many a
supposition has been advanced, of the way in which air might be
conveyed or generated underneath it.
On material circumstance has however generally escaped
observation: namely, that the air to which the rising of this
island has been attributed, is not collected in a body underneath
it; but interspersed through the whole mass: not causing it to
float 'as a reversed saucer would in a bowl of water;' but by
enlarging its bulk, and thereby diminishing its specific gravity.
And the most probable con-
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