OF THE RIVER SAINT LAWRENCE. 



277 





the summer season a scanty, shallow stream, a succession of long pools and ripples, with 

 a current alternately sluggish and rapid, with bars in the upper part of it consisting of 

 gravel, and in the lower part of shifting sand. 



The rain fall of the Ohio Valley may, perhaps, slightly exceed that over the average 

 of the St. Lawrence Valley, as far as we have the means of calculating (the average fall 

 over its area being, perhaps, fifteen per cent, more than that of the St. Lawrence basin) ; 

 yet the range between extreme low and extreme high water is about forty-five feet 

 throughout the river. At Wheeling, Virginia, eight hundred and ninety miles above its 

 junction with the Mississippi, it is forty-five feet ; at Louisville, forty-two feet on the 

 Falls, and sixty-four feet below them ; at Evansville, forty feet ; at Paducah, fifty-one 

 feet ; and at its confluence with the great Mississippi, fifty-one feet. The usual range 

 does not exceed twenty-five feet. The usual rise in the Ohio takes place in February, 

 and occasionally as late as March. This arises from the melting of the snows, and gener- 

 ally amounting to twenty-five feet ; the river remains high for about six weeks. Another 

 rise takes place in May, or June, due to the summer rains, lasting from three to four 

 weeks at Cairo, and from one to two at Louisville. In October, the lowest stage is ob- 

 tained, when it is navigable chiefly for boats of eighteen inches draught; but in Novem- 

 ber, the river generally begins to rise, and continues to do so until the banks are full. 

 These floods are due to the autumn rains, which are sometimes continued as late as the 

 end of December. 



The author is indebted for the foregoing information to a very valuable report, prepared 

 by General A. A. Humphreys, of the United States Army, — a document which has been 

 prepared with the utmost care, and which is calculated to take a prominent position in 

 the literature of our profession relating to hydrodynamics, not only on account of the 

 importance of the questions which are here reported upon, but also on account of the 

 large amount of knowledge it contributes respecting the Mississippi Delta. 



FLUCTUATIONS OE LEVEL IN THE ELEVATION OP THE 8UKEACE8 IN 



'I'll B ORE AT LAKES. 



It cannot be surprising that suppositions have been entertained as to the existence of 

 tides upon these large masses of water ; and we find in the " Eelations des Jesuites," re- 

 corded in the very interesting correspondence sent to France, between 1660 and 1680, 

 frequent references to the subject. Later than that the subject was noticed by Dr. Weld, 

 in his travels in Canada, from 1790 to 1795, who stated that it was believed by many 

 that the waters of Lake Ontario were influenced by a tide ebbing and flowing frequently 



