202 



FROZEN WELL. 



Fio. 100. 



though small in quantity, we have reason to believe is constantly working its way to the 

 surface? The character of the strata, as they are exhibited at the section laid bare in the 

 road (see Fig. 99), may furnish us with an answer to this question. Some of the layers 

 there, consist of pebbles almost entirely separated from sand, or loam, such as we frequently 

 see on the shores of rivers and the ocean. And the well-diggers testify that such beds 

 were penetrated in making the excavation beneath the frost. Now such materials and 

 the same is true more or less of every deposit of loose materials coarser than impalpable 

 powder must contain a large amount of air in the interstices. The temperature of this 

 air will be raised by the heat coming up from beneath, and being thus made lighter, it 

 will escape into the atmosphere, and its place be supplied by that from abroad, which is 



denser and colder, and that by the same 

 opening through which the heated air 

 escapes, or through any other opening 

 where the gravel comes to the surface. 

 Thus the heated air would be carried off 

 without scarcely coming in contact at all 

 with the frozen mass. It would thus 

 escape, even though the stratum of pebbles 

 were horizontal, at any point where it 



comes to the surface. But it would facili- 

 tate the operation to have the bed inclined, 

 as shown at A (Fig. 100), where C represents the frozen mass, H a layer of clay above it, 

 D the well, and E A a stratum of clear pebbles. F and G show the wells dug by the 

 Boston Society of Natural History. 



Such an arrangement of the materials, similar to that at Brandon, reminds us of the 

 construction of the most improved ice houses and refrigerators. One of our number 

 (A. D. Hager), who first suggested this mode of explaining the preservation of the 

 frozen deposit, has gone into greater detail on the subject, in a letter which will be found 

 in the sequel. 



If air can thus pass beneath such a deposit and convey away the heat that comes up 

 from the interior, it would also exert another influence for the preservation of the ice, viz., 

 by evaporation. The fragments would usually be moist, and often wet, and the inevitable 

 effect of the contact of dry air would be evaporation, and the effect of this would be cold. 

 Even though the motion of the air be very slow, these effects must take place, viz., 

 evaporation and cold. If we exclude the idea of heat rising from the interior of the 

 earth and thus causing the air to escape from the porous earth, while the external air 

 of greater density takes its place, yet the changes of temperature in the external air 

 must produce more or less of movement in the air that exists in the gravel and sand, 

 admitting it to have a communication with that above the ground. These underground 

 currents, whose existence is thus demonstrated, even though slight and slow, must produce 

 evaporation and cold how much, would depend on circumstances. But taking all the 

 facts into account, some of us are disposed to impute a more powerful influence to 

 evaporation, both in the production and preservation of subterranean cold, than to the 

 non-conducting power of the materials. 



