Great North American Lakes. 87 



for a place among your data. The slight information con- 

 veyed m the conversation to which you refer, and in the nar- 

 rative in your possession, was furnished by memory. At the 

 present moment, as far as that extends to observations made 

 at so distant a period, it tells me, that each time and place 

 of making the experiment, illustrated the fact in its general 

 outline, without giving it the distinctness and uniformity I 

 sought ; and without separating it from certain proximate 

 agents, whereby the same result might have been produced 

 by more obvious and sensible causes. 



At two of these places, the Black River and Fort Howard, 

 large rivers disembogue themselves, and at another, Fort 

 Gratiot, a lake. They seem to present the fairest points for 

 experiment. If in such places there appear occasional ele- 

 vations and depressions of the water, or alternate accelera- 

 tions and retardations of the stream, the pressure from above 

 would seem to be resisted by a new agent, and an inward 

 current imperviable at once. I know nothing of a variation 

 of the force of the stream, on its outward passage ; but a 

 periodical difference in the altitude of the water was, at the 

 time and places of my experiments indisputable. I placed 

 and removed the graduated rod with my own hand ; and at 

 stated periods noticed the rise and fall, of which a clear and 

 determinate impress is left upon my memory. 



But at the time of making these experiments, two subor- 

 dinate cicumsicmces presented themselves ; the one of them, 

 the wind, the action of which might have forced in or out 

 of the mouths of the rivers a greater or less quantity of 

 water, and that accounted for the difference in its elevation. 

 The other, the force of the current, or the bulk of the water, 

 which might have been increased, or diminished by the dif- 

 ference, between the daily and nightly discharges of the 

 fountains, which afford a supply from above. If the quantity 

 poured forth at one period was greater than at another, the 

 volume itself accounted for the occasional elevation. If the 

 actual increase of the element was not proportioned to the 

 apparent increase of its bulk, still the impulse given to the 

 current, in the centre, by the increase of force from above, 

 might create an increase of counter-current at the margin, 

 and force the water higher up. These are the possible causes 

 to which I have just referred. If any weight be attached 

 to them, and I know not that they are worthy of any, the 

 rise and fall of the water may be accounted for, without the 



