the place of observation or at some distant points. A local
increased pressure of the atmosphere at the place of observation would
lower the water level, where there is a wide expanse of water; or a
diminished pressure, under the same circumstances, would cause the
water to rise above its usual level."

In the summer of 1834, according to the report of Foster and Whitney,
made to Congress, in 1850, an extraordinary retrocession of the waters
took place at Saut St. Mary. The river here is nearly a mile in width,
and the depth of the water over the sandstone rapids is about two and
a half feet. The phenomenon occurred at noon. The day was calm but
cloudy; the water retired suddenly, leaving the bed of the river bare,
except for the distance of about twenty rods where the channel is
deepest, and remained so for the space of an hour. Persons went out
and caught fish in the pools formed in the rocky cavities. The return
of the waters was sudden and presented a sublime spectacle. They came
down like an immense surge, roaring and foaming, and those who had
incautiously wandered into the river bed, had barely time to escape
being overwhelmed. A similar event occurred in 1842, when the current
set back from the rapids, and the water rose upward of two feet above
the usual mark.

In 1845, Foster and Whitney, while coasting in an open boat between
Copper Harbor and Eagle River, observed the water rise up, at a
distance of a fourth of a mile to the northwest, to the height of
twenty feet. It curled over like an immense surge, crested with foam
and swept toward the shore. It was succeeded by two or three swells of
less magnitude, when the lake resumed its former tranquillity. At the
same time the mirage was beautifully displayed, and imaginary islands
were seen along the horizon. In 1849, they witnessed at Rock Harbor,
Isle Royale, the ebbing and flowing of the water, recurring at
intervals of fifteen or twenty minutes, during the entire afternoon.

The difference between the temperature of the air and the lake, gives
rise to a variety of optical illusions known as _mirage_. Mountains
are seen with inverted cones, headlands project from the shore where
none exist. Islands clothed with verdure or girt with cliffs rise up
from the bosom of the lake. On approaching Keweenaw Point, Mount
Houghton is the first object to greet the eye of the mariner. In
peculiar stages of the atmosphere, its summit is seen inverted in the
sky long befo