10 



APPENDIX TO THOMPSON'S VERMONT 



SHELBURNE BAT. 



LiKE CHA3IPLAIN PHENOJ^ENA. 



The following record, kindly furnished 

 me by my friend Robert Vvhite, Esq., of 

 Shelburne, exhibits the number of days, 

 during which teams were able to pass upon 

 the ice from Shelburne Harbor across the 

 mouth of Shelburne Bay and the southeast- 

 ern part of Burlington Bay, to Burlington, 

 in each year since 1835. 



Lake Champlain Phenomena. 



In Part I, page 14, something was said 

 respecting the sudden disappearance of the 

 ice from Lake Champlain in the spring of 

 some years, and an attempt was made to 

 account for the phenomenon, without hav- 

 ing recourse to the absurd notion that the 

 ice sinks. The explanations there given 

 were founded, partly on observed facts, and 

 partly on theoretic views. Additional ob- 

 servations have since been made, wliich, 

 while they go to confirm the general theo- 

 retic principles, require some modifications 

 of the results. It was there supposed that, 

 when the general surface of the lake com- 

 menced freezing, the great body of the 

 water below might be at a temperature 7^ 

 or 8^ above the freezing point, and this, in 

 accordance with the researches of Count 

 Rumford, would doubtless be true were the 

 waters gradually cooled down without agi- 

 tation. But it is not found to be true in 

 fact ; and from recent observations it ap- 

 pears probable that, in consequence of their 

 violent agitation by the cold winds which 

 prevail in the early part of winter, the 

 whole mass of water is cooled down very 

 nearly to the freezing pomt before any ice 

 is formed at the sui-face over the deeper 

 parts of the lake, and that, after the waters 

 are protected from the winds by a covering 

 of ice, their temperature is gradually, but 

 slowly, elevated by the reception of heat 

 from the earth beneath. The following ex- 

 periments show that the temperature of the 

 water under the ice is, generally, some de- 

 grees above the freezing point, but not so 

 much above as we had supposed. 



On the 27th of March, 1844, when the 

 lake had been covered with ice about eight 

 weeks, at the distance of one-fourth of a 



' The mouth of Shelbiu-ne Bay only. 



mile from the shore, the temperature of the 

 water was found to be, at the surface 32'=, 

 at the depth of 6 feet 32^-— at 12 feet 34^ 

 and at 25 feet 35i°. On the 8th of Mai'ch, 

 1852, when the lake had been frozen over 7 

 weeks, one-fourth of a mile from the shore, 

 where the water was 28 feet deep, the tem- 

 perature at the bottom was 34i°, that at the 

 surface being 32^. On the 5th of April 

 following, at the distance of one mile from 

 the shore, the water being 82 feet deep, the 

 temperature at the bottom was 34"'. At 

 the distance of 2 A miles from the shore, at 

 an open crack where the water was 125 feet 

 deep, the temperature at the bottom was 

 34.^^. 



The sudden disappearance of the ice from 

 Lake Champlain has been a subject of re- 

 mark and speculation, from the first settle- 

 ment of the country. But to a person, who 

 carefully observes the circumstances, there 

 will not appear any thing in the phenome- 

 non either mysterious or very wonderful. 

 In order to its occurrence, the temperature 

 of the great body of water must be some 

 degrees above the freezing point, the ice 

 must be reduced to the honey-comb struc- 

 ture, or bi-ought into a condition in which 

 it will easily sepai-ate into minute divisions, 

 and there must be a wind sutficiently strong 

 to produce considerable agitation of the 

 water. 



In addition to theoretic objections to the 

 popular notion that the ice sinks, when it 

 disappears suddenly ,persons of observation, 

 who live near the lake, have occular proof 

 that it does not sink. The ice, while yet 

 spreading over the entire surface of the 

 lake, is seen to be gradually wasting as 

 spring advances and to become less firm, 

 till, at length, it is so far disintegrated that 

 a stick may be thrust through it, while it 

 is yet from 6 to 12 inches thick. This dis- 

 integration is sometimes carried so far, 

 before the general icy covering is broken 

 up, that the ice has little more solidity or 

 tenacity than snow saturated with water. 

 In this state of things, a strong wind soon 

 pi'oduces rents in the ice, — the waters,_ be- 

 fore pent up and quiet, are thrown into 

 violent agitation, and the slightly cohering 

 masses are actually seen falling to pieces 

 and dissolving on the surface of the water. 

 But it is never seen sinking, nor was any 

 ever seen lying at the bottom afler it had 

 sunk. 



Some have supposed that the sudden ab- 

 sorption of so large an amount of caloric, 

 as would be required for the liquefaction 

 of the ice, would produce severe frost in 

 the neighborhood of the lake, which is not 

 found to be true in fact. But this difficulty 

 is removed by the consideration, that the 

 heat employed in melting the ice, is derived 



