172 Scientific Intelligence — Hydrography, 



HYDROGRAPHY. 



3. On the Phenomena of the Rise and Fall of the Waters of the 

 Northern Lakes of America. — At a meeting of the American Aca- 

 demy, February 1849, Mr Foster, of the United States Mineral 

 Survey in the North-west Territory, presented the result of some ob- 

 servations, undertaken with a view of determining whether the waters 

 of the northern lakes are subject to any movements corresponding to 

 tidal action. The result of these observations had convinced him 

 that these waters do not rise and fail at stated periods, correspond- 

 ing to the ebb and flow of the tide, but are subject to extraordinary 

 risings, which are independent of the influence of the sun and moon. 

 These risings attracted the attention of the earliest voyageurs in 

 these regions. Charlevoix, who traversed the lakes nearly a century 

 ago, says, in reference to Lake Ontario : — " I observed that in this 

 lake there is a sort of reflux and flux almost instantaneous ; the 

 rocks near the banks being covered with water, and uncovered again 

 several times in the space of a quarter of an hour, even if the sur- 

 face of the lake was very calm, with scarce a breath of air. After 

 reflecting some time on this appearance, I imagined it was owing to 

 springs at the bottom of the lake^ and to the shock of their currents 

 with those of the rivers which fall into them from all sides, and 

 thus produce those intermitting motions, ^^ The same movements 

 were noticed by Mackenzie in 1789 ; by an expedition under Colonel 

 Bradstreet in 1764; on Lake Erie in 1823, and at various later 

 periods. In the summer of 1834, an extraordinary retrocession of 

 the waters of Lake Superior took place at the outlet of Sault St Marie. 

 The river at this place is nearly a mile wide, and in the distance of 

 a mile falls 18*5 feet. The phenomena occurred about noon. The 

 day was calm, but cloudy. The water retired suddenly, leaving the 

 bed of the river bare, except for a distance of thirty rods, and re- 

 mained so for nearly an hour. Persons went out and caught fish 

 in pools formed in the depressions of the rocks. The return of the 

 waters is represented as having been very grand. They came down 

 like an immense surge, and so sudden was it, that those engaged in 

 catching fish had barely time to escape being overwhelmed. In the 

 summer of 1847, on one occasion the water rose and fell at intervals of 

 about fifteen minutes during an entire afternoon. The variation was 

 from twelve to twenty inches, the day being calm and clear ; but the 

 barometer was falling. Before the expiration of forty-eight hours, 

 a violent gale set in. At Copper harbour, the ebb and flow of the 

 water through narrow inlets and estuaries has been repeatedly noticed 

 when there was not a breath of wind on the lake. Similar pheno- 

 mena occur on several of the Swiss lakes. Professor Mather, who 

 observed the barometer at Copper harbour during one of these fluc- 

 tuations, remarks -. — " As a general thing, fluctuations in the baro- 

 meter accompanied fluctuations in the level of the water ; but some- 



