No. 392.] AN ABNORMAL WAVE IN LAKE ERIE. 657 
has subsided, the gradually diminishing undulations may con- 
tinue for some time. These undulations are known as the 
“swell.” 
From time to time observers near lakes have noticed move- 
ments in their waters which could not be classed as ordinary 
waves. Any such unusual rise of water is popularly termed a 
“tidal wave,” but in reality the tides in lakes are too slight to 
be detected by any but the most delicate observations. It is 
much more probable that such disturbances are caused in one 
of the following ways : 
When a heavy wind blows nearly parallel to the length of a 
rather narrow lake for a day or so, the waters move with it and 
rise on the shore against which they are driven. In November, 
1892, a storm from the west caused the waters of Lake Erie, 
near Toledo, to fall eight or nine feet below the normal fair- 
weather level. At the same time unusually high water was 
experienced at the eastern end of the lake. ; 
Sudden changes in the outlet of a lake may produce changes 
in the level of its water; as when an outlet is dammed by an 
ice gorge or by an avalanche. 
Earthquakes produce waves in bodies of water, but there are 
no instances recorded of such waves in lakes. 
A seiche is a change of level in the waters of a lake, supposed 
to be due to changes of barometric pressure on different por- 
tions of the water surface. There are also certain rhythmical 
pulsations, producing a difference of level of three or four 
inches during calms, when no similar variation of atmospheric 
pressure can be detected. 
The seiche has been quite thoroughly studied in the lakes of 
Switzerland, particularly by Forel, but although similar move- 
ments are known to occur in our great lakes, the subject here 
is one which awaits investigation. 
The rise of the waters of Lake Erie, under consideration, 
was evidently one of these exceptional movements of large water 
bodies, and by noting the conditions under which it took place 
we may be able to gain some knowledge as to their causes. 
Was it an earthquake wave ? 
We can be almost certain that it was not; for if any earth- 
