280 



ON THE HYDROLOGY OF THE BASIN 



velocity at the point first mentioned being increased from three and a quarter to six and 

 a half miles per hour. 



Up to the present time there have, unfortunately, been very few opportunities of ob- 

 taining these observations by any special scientific or professional investigation. 



The fluctuations in these lakes have of late formed the subject of very careful investi- 

 gation and daily observation ; and ever since the establishment of the canals, records have 

 been kept from which it is easy to describe the curves of fluctuation. Colonel Whittlesea, 

 of the State Survey Department, at Cleveland, Ohio, has given much attention to the 

 history of water-levels, as far back as 1788; and the results of modern observations, and 

 of all his own inquiries, which seem to embrace everything that could be collected from 

 trustworthy sources in the United States, are given in a very valuable memoir by that gen- 

 tleman, published in the Smithsonian contributions, dated July, 1860. 



But Mr. Whittlesea, like most others who had considered the probability of a tide 

 existing in these lakes, appears to have failed to discover direct evidences of a flux and 

 reflux that could be connected with the moon's motions. 



Such observations, however, from the fitful state of the weather over the whole of this 

 region, would require unusual attention and fitting opportunities for observations with 

 most critical accuracy, for which is required the aid of appliances, and a residence for 

 some time on the spot, to determine and estimate the quantities, which necessarily could 

 only be small. And it is not surprising that those who, like Mr. George C. Davis, 

 and Mr. Jonathan Carver (who were probably but ill supplied, in 17G6, with suitable 

 instruments for exact observation), failed to observe any diurnal flood and ebb in the 

 upper lakes. 



It remained for Lieutenant-Colonel Graham, of the United States Topographical Engi- 

 neers, in charge of the works on Lake Michigan and Lake Superior, positively to affirm 

 the existence of the truth which was first stated by him in JS'ovember, 1858. Since that 

 time the subject has been steadily occupying the attention of Colonel Graham, and of his 

 staff; and the results are given in the report of the Topographical Bureau, for the year 

 1860 (dated September 30th). The course of the observations has included the recorded 

 ordinates of a curve indicated by tide-gauges ; and the discussion of these variations has 

 included a very careful examination of exact meteorological records, in conjunction with 

 these phenomena. The result may be stated broadly, that at Chicago, on Lake Michigan, 

 there was a semi-diurnal spring tide of T y o 4 „ of a foot, and a semi-diurnal mean tide of 

 ,'„',;'„ of a foot. Similar observations conducted by Captain Meade, of the United States 

 Topographical Engineers, show that in Lake Superior, at Superior City, the semi-diurnal 

 spring tide is equal to 0.169 of a foot, and the semi-diurnal mean tide to .087 of a foot. 

 This quantity is, of course, very small, and beyond a scientific interest, is of no practical 



