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On the disappearance of the Ice on Lake Champlaiji. 23 



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tainly not more than three or four), in which the lake has been en- 

 tirely covered with ice on one day, and entirely clear of ice on the 

 next. One case only of this kind has occurred within the period 

 of my own observations, and that took place about twenty years 

 since. The ice at that time, though of considerable thickness, had 

 • become exceedingly porous and rotten, and for some days had 

 been considered unsafe; but, having been stifferjed at its surface 

 by a sharp frost in the night, some persons ventured upon it in the 

 morning, and passed safely over the lake on foot, where the width 

 is six or seven miles; but during the day a storm set in, with a 

 very strong wind, and, on the following morning, the ice had 

 entirely disappeared ; there Avas none to be seen on the lake. 



Now an occurrence of this kind is certainly calculated to excite 

 wonder in the mind of the general observer, and make the sud- 

 den clearing of the lake a common topic of conversation ; but it 

 appears to me that all the mystery about the matter vanishes at 

 once whenever the circumstances are carefully considered. These 

 circumstances I have stated in general terms in Part I, p. 14 of 

 my Nat. and Civil Hist, of Vermont, published in 1842. But ex- 

 periments and observations made since that time require me to 

 modify some of the statements there presented. It was then sup- 

 posed that, when the ice commenced forming upon the surface o{ 

 the lake, the great body of water below was at a temperature of 

 about 39^ or"4lF. This, according to the researches of Count 

 Rum ford, would doubtless be true were the waters cooled down 

 without agitation ; but I find it is not true in fact, and from the 

 observations I have made, I am now inch'ned to the opinion that, 

 in consequence of their violent agitation by the cold winds which 

 prevail in the early part of winter, the whole mass o( waters is 

 usually cooled down very nearly to the freezing point before any 

 ice forms at the top, and that, after the waters are protected from 

 the winds by a covering of ice, their temperature is gradually 

 raised by the reception of heat from the earth beneath, 



Sirjce the publication of my history of Vermont I have made 

 ^ some experiments for the purpose of ascertaim'ng the temperature 



of the water of the lake at various depths, after it had been for 

 some time entirely covered with ice. In all these I have found 

 the temj)erature some degrees above freezing, but not quite so 

 much above as I had previously supposed- As an example, I copy 

 the following record from my meteorological journal for 1844 : 



"March 27. Temperature of the water of the lake in contact 

 witli the ice, 32^ ; six feet below the surface, 32|^ ; twelve feet 

 below, 34^^; and twenty-jive feet below, being the whole depth 

 of the lake at that place, 35^^/' These observations were made 

 nearly one-fourth t)f a mile from the shore, and after the lake had 

 been covered with ice about eight weeks. 



It has long been my intention to ascertain the temperature at 

 the bottom of the deeper parts of our lake when covered with ice, 



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