10 FLUCTUATIONS OF LEVEL 



duiin<; the mouth ; the course and strength of the wind were recorded, with occa- 

 sional observations of the barometer. 



The mean elevation of Lake Superior above Lake Huron is not yet known, 

 nor tlie precise difference of elevation at any one time. 



It is evident that tlie mean elevation of Lake Erie, or any of tlie Lakes above 

 the ocean, cannot be determined till the mean of its fluctuations are known. We 

 call the height of Lake Erie five hundred and sixty-five feet above mean tide at 

 Albany, because it was found to be so at the time when the Erie Canal was sur- 

 veyed. But without knowing the state of the water 'at Black llock or Buffalo at 

 that day, it is evident there may be an error of two and a half to three feet. 



The same may be said of all the Lakes. The rise to be overcome by the canal 

 at the Falls of St. Mary's was reported by the engineers to be seventeen and one- 

 half feet ; but if there is a change of level in Lake Superior above the falls, it does 

 not follow, as has been just observed, that the same change of level would be 

 noticed below the falls where the river is wider. 



Mr. Murray, of the geological survey of Canada, in 1848, examined the other 

 rapids of the St. Mary's river, and made their united descent two feet JJ^ths, 

 which, added to the above and neglecting the descent of the water between the 

 rapids, the difference is twenty feet j%\. As measured barometrically by Captain 

 Bayfield, the elevation of Lake Superior is six hundred and twenty-seven feet 

 above the ocean, and Lake Huron is stated by Mr. Iliggins to be five hundred and 

 seventy-eight, making a difference of forty-nine feet. 



The elevation of Lake Huron is, however, subject to correction by future levels 

 along the connecting straits. 1 have not, in this paper, given the details of the 

 water tables, reserving them for publication within their respective States. The 

 results are shown in the proper tables, in the form of a monthly average, witli 

 remarks. 



The register of Messrs. Finney and Sherwood for the six summer months of 

 1855 and 185G, show a difference between the depth of water at the lower and at 

 the upper locks of about ten inches during those years, as follows : — 



Feet. Indies. 



Mean depth of water at Upper lock six months, 1855 .... 12 It. 00 



185G .... 12 10.25 



lower loek si.\ months, 1855 . ... . 12 00.38 



1856 .... 12 1.00 



These tables show conclusively the effect of winds in raising and depressing 

 the water in a narrow and crooked strait connecting two Lakes. On the morning 

 of July 16, 1855, the wind was from the northwest, and oft" I^ake Superior. As 

 usual, in that case, the water rose at the upper gate, varying from twelve feet one 

 inch to thirteen feet six inches, or about one and one-half feet. 



At noon the wind had changed to the opposite quarter and blew from the 

 southeast. The water fell to eleven feet five inches, and at one F. M. to ten feet 

 nine inches, making a difference of two feet nine inches in less than eight hours. 



On tlie od of June, 185(5, the observers witnessed a still more remarkable change, 

 because it occurred wliile the wind was steadily from the same quarter. It blew a 



