NATURAL PHILOSOPHY. 157 



Experiments since made by Professor W. Thompson have verified 

 the prediction, and it may now be considered as established, that the 

 effect of pressure on water, and all other liquids which like it expand 

 in freezing, is to lower their freezing point ; and that a reverse effect, 

 or an elevation of the freezing point by an increase of pressure, may 

 be expected for all liquids which contract in freezing. The extent of 

 the effect to be expected may in every case be deduced from Regnault's 

 obsp.rvations on vapor, if the latent heat of a cubic foot of the liquid, 

 and the alteration of its volume in freezing, be known. Brewster's 

 Philosophical Magazine, Aug. 



THE EXUDATION OF ICE FROM THE STEMS OF VEGETABLES, 

 AND THE PROTRUSION OF ICY COLUMNS FROM CERTAIN 

 KINDS OF EARTH. 



AT the meeting of the American Association at Charleston, an 

 elaborate and important paper was read by Prof. John Le Conte " on 

 a remarkable exudation of ice from the stems of vegetables, and on a 

 singular protrusion of icy columns from certain kinds of earth during 

 frosty weather." After referring to the little attention which phe- 

 nomena of this nature have received, the author states that in a visit 

 to the sea-coast of Georgia, in November, 18-18, he had an opportunity 

 of observing the remarkable deposition of ice around the stalks of cer- 

 tain plants, especially in the two species Pluchea bifrons and P. cam- 

 phorala, both of which grow abundantly in wet soils, and along the 

 road-side ditches of that section. The exudations are most abundant 

 during the first clear frosty weather in November and December, when 

 the earth is warm, and there is considerable difference between the 

 temperature of the day and the night. When the temperature sinks 

 towards daylight to about 28 or 30 3 F., or even lower, the surface of 

 the ground is totally devoid of the slightest incrusting film of frozen 

 earth, while hoar-frost is deposited in great profusion on all dead veg- 

 etable matter. At a distance, the accumulations of voluminous friable 

 masses of semi-pellucid ice around the footstalks of the Pluchea pre- 

 sent the appearance of locks of cotton-wool, varying from four to five 

 inches in diameter. 



The observations made by Prof. Le Conte appear to establish the 

 following facts. 1. The depositions of ice are confined to the imme- 

 diate neighbourhood of the roots of the plants, frequently commencing 

 two or three inches from the ground, and extending from three to four 

 inches along the axis of the stem. At this season the stalks are dead 

 and dry to within about six inches of the earth, below which they are 

 green and succulent, and the plant has a large porous pith, which is 

 always saturated with moisture as high as six or seven inches from 

 the base of the stern. 2. The ice emanates in a kind of ribbon or 

 frill shaped, wavy, friable, semi-pellucid excrescence, " as if protruded 

 in a soft state from the stem, from longitudinal fissures in its side," 

 as described by Sir John Herschel, who noticed a similar phenomenon 

 in the heliotrope. ' ; The structure of the ribbons is fibrous, like that 

 of the fibrous variety of gypsum, presenting a glossy silky surface, 



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