14 



NATURAL HISTORY OF VERMONT. 



Part I. 



OPENING AND CLOSING OF LAKE CHAMPLAIN. 



DISAPPEARANCE OF THE ICE. 



vegetation is protected by the morning 

 fogs for some time after its growth has 

 been stopped upon the uplands. The 

 early part of the autumn is usually pleas- 

 ant and agreeable and the cold advances 

 gradually, but as it proceeds the changes 

 become more considerable and frequent, 

 and the great contrast between the tem- 

 perature of the day and niglit at tliis sea- 

 son render much precaution necessary in 

 order to guard against its injurious effects 

 upon health. The ground does not usu- 

 ally become much frozen till some time 

 in November, and about the ;25th of that 

 month the ponds and streams begin to be 

 covered with ice, and the narrow parts of 

 lake Cliamplain become so much frozen 

 as to prevent the navigation from White- 

 hall to St. Johns, and the line boats go in- 

 to winter quarters, but the broad portions 

 of the lake continue open till near the first 

 of February, and the ferry boats from Bur- 

 lington usually cross till the first of Jan- 

 uary. The following table contains the 

 times of the closing and the opening of 

 the broad lake opposite to Burlington, 

 and wlien the steamboats commenced and 

 stopped their regular trips through the 

 lake from Whitehall to St. Johns, for sev- 

 eral years past : 



It frequently happens that the ice con- 

 tinues upon the lake for some time after 

 the snows are gone in its neighborhood 

 and the spring considerably advanced. 

 In such seasons the ice often disappears 

 very suddenly, instances having been 

 observed of the lake being entirely cov- 

 ered with ice on one day and the ne.xt day 

 no ice was to be seen, it all having dis- 

 appeared in a single nigiit. People in the 

 neighborhood, being unable to account for 

 its vanishing thus suddenly in any other 

 way, have very generally supposed it to 

 sink. This opinion is advanced in the 

 account of this lake contained in Spaf- 

 ford's Gazetteer of New York, and the 

 anomaly is very gravely attempted to be 

 accounted for on philosophical principles. 

 But the true explanation of this phenom- 

 enon does not require the absurdity of the 

 sinking of a lighter body in a heavier. It 

 is a/> simple result of the law by which 

 heat is propagated in fluids. That bodies 

 are e.xpanded, or contracted, according to 

 the increase or diminution of the heat they 

 contain, is a very general law of nature. 

 Fresh water observes this law, when its 

 temperature is above 40°, but below 40" 

 the law is reversed, and it expands with 

 the reduction of temperature. 



When winter sets in, the waters of the 

 lake are much warmer than the incum- 

 bent atmosphere. The surface, therefore, 

 of the water communicates its heat to the 

 atmosphere, and, becoming heavier in 

 consequence, sinks, admitting the warmer 

 water from below to the surface. Now 

 since heat is propagated in fluids almosten- 

 tirelybythe niotion of the fluids, this cir- 

 culationwill go on, if the cold continues, till 

 all the water from the surface downward 

 to the l)ottom is cooled down to the tem- 

 perature of 40°. It will then cease. The 

 colder water now being lighter than that 

 below, will remain at the surface and soon 

 be brought down to the freezing point and 

 congealed into ice. This accounts for the 

 ice taking soonest where the water is most 

 shallow, and also for the closing of the 

 broad parts of the lake earliest in tliose 

 winters in which there is most high wind, 

 the process of cooling being facilitated 

 thereby. 



Af"ter the ice is formed over the lake, 

 and durino- the coldest weather, the great 

 mass of water, after getting a few inches 

 below the ice, is of a temperature 8° above 

 the freezing point. While the cold is se- 

 vere, the ice will continue to increase in 

 thickness, but the mass of water below 

 the ice will be unaffected by the tempera- 

 ture of the atmosphere above. Now the 

 mean annual temperature of the climate 

 in the neighborhood of lake Champlain 



