Jrom the Stems of J^egetahles, 9S9 



planation of them. Before doing so, it may be well to premise, 

 that whatever may be thought to be the proximate cause of 

 these phaenomena, all the rules of philosophizing require us to 

 look to the earth for the supply of fluid, and to the influence 

 ai cold for the elevating force. We have seen that the effect 

 is invariably connected with cold, that it increases or dimi- 

 nishes witii the intensity of the frigorific influence, and that it 

 is proportional to the depression of temperature in all cases 

 of tmimpeded action. The whole difficulty lies, therefore, in 

 ascertaining the modus operandi of this cause, „, 



After considerable reflection, we venture to offer the fol- 

 lowing as the most probable explanation of the phsenomenon. 

 Let us suppose a portion of tolerably compact porous and 

 warm earth, saturated with moisture, to be exposed to the 

 influence of a cold-producing cause. The soil being an indif- 

 ferent conductor of heat, only a very superficial stratum would 

 be reduced to the freezing-point. As the resistance to lateral 

 expansion is less at the surface than it is at a sensible depth 

 below, the effect of the first freezing would be to render the 

 apices of the capillary tubes or pores conical or pyramidal. 

 The sudden congelation of the water filling the conical capil- 

 laries in the superior stratum would produce a rapid and for- 

 cible expansion, which, being resisted by the unyielding walls 

 of the cone, would not only protrude, but jn^qject or detach 

 and throw out the thread-like columns of ice in the direction 

 of least resistance, or perpendicular to the surface. This 

 would leave the summits of the tubes partially empty, — a con- 

 dition essential to the development of capillary force. Under 

 these circumstances, capillary attraction would draw up warm 

 water from beneath, which, undergoing congelation, would in 

 like manner elevate the column of ice still higher; and thus 

 the process would go on as long as the cold continued to 

 operate on unobstructed capillaries supplied with sufficient 

 water from below. It will be remarked, that this explanation 

 makes the whole process of protrusion to take place in a stra^* 

 tum of earth of almost inappreciable thickness. It also pre- 

 sumes that the protruding force acts paroxysmally. Does not 

 the 'iioavy striated structure of the icy columns clearly indicate 

 that the freezing process is intermittent 'i It is obvious that 

 the unfrozen state of the soil is maintained through the opera- 

 tion of two causes ; to wit, the unceasing supply of warm water 

 from below, and the large amount oHatent heat evolved during 

 the continued process of congelation. These two causes ap- 

 pear to be fully adequate to explain this remarkable fact. 



The foregoing view explains why the phaenomenon does not 

 take place on hard- beaten earth and on very loose soils ; for, 



