282 Schermerhorn—Northern and Northwestern Lakes 
Ontario, 84 inches. This is about equal to 31 inches on the 
entire lake basin. 
‘ The following represent the average discharges at the outlets 
of the lakes: : 
Lake Superior, at St Mary’s River ___._.-- 86,000 cu. ft. per. sec. 
Lakes Michigan and Huron,at St.Clair river, 225,000 “ ce 
akephinve. atuNitacaray heen eer sae ee 2655000) Wise ce 
Lake Ontario, at St. Lawrence river____- 300,000 <“* es 
The aggregate discharge of the lakes is double that of the 
Ohio and nearly equals half the discharge of the Mississippi. 
The area of the lake basin is a third larger than the basin of 
the Ohio, or about a fifth the combined areas of the basins of 
the Mississippi and its affluents. The outflow of the lake basin 
is-slightly less than half the rain fall, while on the Mississippi 
and Ohio the discharge is about a fourth the rainfall. If the 
average discharge of the lakes passed through a river one mile 
wide with a mean velocity of one mile per hour, such a river 
would have a depth of 40 feet from shore to shore. 
The volume of water in the lakes is about 6000 cubic miles, 
of which Lake Superior contains a little less than one-half. 
Perhaps a better idea of this volume may be obtained when it 
is said that it would sustain Niagara Falls in its present con- 
dition for about 100 years. 
In relation to the depth of water on the crest of Niagara 
Falls it can be easily demonstrated that if the water passed 
over the Falls in a sheet of uniform thickness for the entire 
length of the present water way, which is about 3600 linear feet, 
the depth of the sheet would not exceed 4 feet. It is highly 
probable that at the apex of the Horseshoe Falls the depth is 
nearly 20 feet, consequently it may be inferred that the depth 
of the sheet except in a few places is less than 4 feet. 
The principal changes in the elevation of the lake surfaces 
are those due to the wind and to rainfall. Prof. Whittlesey 
states that on Aug. 18, 1848, a gale from the N.E. reduced the 
water level at Buffalo, N. Y., toa point 154 feet lower than the 
surface of the lake on Oct. 18, 1849, at which time a terrible 
gale occurred fromthe S.W. ‘This was an excessive difference 
of level and one of rare occurence 
During protracted autumn gales waves have been observed 
which through reliable means, measured from 15 to 18 feet 
above the normal surface. 
The second class of variations, those due to rainfall, occur 
with considerable regularity. The lowest water in the year 
generally occurs in Lakes Ontario, Erie, Michigan and Huron 
in the months of November and March, and on Superior in 
March. The highest water occurs on the first named lakes in 
