from the Stems of Vegetables. 337 



variance with the idea of the phfleromenon being a modifi- 

 cation of hoar-fiost, but the amount of water congealed at 

 the surface during a single night is vastly too great to have 

 come from this source. Moreover, the phsenomenon occurs 

 very conspicuously during our most violent and dry north- 

 west winds ; circumstances under which it would be impos- 

 sible for any condensation of atmospheric vapour to take place. 

 It is well known to meteorologists, that a rapid agitation of 

 the lower strata of the atmosphere totally subverts the con- 

 dition which is most essential to the deposition of dew, namely, 

 that the surface must be colder than the superincumbent air. 



2. It cannot be occasioned by the cold contracting a super- 

 ficial stratum of earth, and thus forcing up the moisture which 

 freezes at the surface, because this cause is utterly inadequate 

 to furnish the large supply of fluid which is required for the 

 production of columns of ice from three to five inches in length. 

 The fact that isolated clods lying in moist situations frequently 

 exhibit a protruded investment of icy columns quite equal in 

 volume to the mass of earth from which they issued, is obvi- 

 ously and palpably at variance with this idea. The phaeno- 

 menon observed on the stems of plants is likewise manifestly 

 inconsistent with this notion. 



3. It cannot be owing to the exhalation of aqueous vapour 

 from the comparatively warm earth beneath through spiracles, 

 undergoing condensation and congelation at the surface, and 

 thus protruding the columns ; for the amount of evaporation 

 from such a surface, when the temperature of the air is at 12 

 or 14; degrees of Fahrenheit's scale, is hopelessly inadequate 

 to furnish the necessary amount of water. Frequently during 

 a single night a sufficient quantity of moisture is elevated in 

 the form of icy columns to maintain the surface in a very wet 

 condition, even after several days' exposure to the sun. 



4. Neither can the protrusion of the columns of ice be as- 

 cribed to the mere expansion of water during the act of freezing 

 iu the capillary tubes in the clay ; for this supposition is op- 

 posed to the well-established fact, that they are not connected 

 with any formation of ice below. Besides, if we assume the 

 specific gravity of ice to be '92 as compared with water at 

 32° F., it follows that the amount of expansion which it un- 

 dergoes during the process of congelation is about 87 parts 

 in lOOQ by volume. Granting the rigidity of the capillary 

 tubes to be such as to admit of no transverse increment, and 

 that the whole amount of cubic expansion is thereby mani- 

 fested in the longitudinal extension of the column, it appears, 

 from a simple calculation, that to protrude three inches of ice 

 the frozen column must penetrate about thirty four inches be- 



