188 Dr. M^Keever on the [March, 



through some weak part, through which the water escapes, and 

 subsides to its former level, leaving the singular appearance of 

 a wall or rampart of ice, three or four feet high, and about two 

 feet in thickness, along the greatest part of the upper edge of the 

 weir. The ice composing this barrier, where it adheres to the 

 stone, is of a solid consistency, but the upper part consists of a 

 multitude of thin laminae, or layers resting upon each other, in a 

 confused mamier, and at different angles of inclination, their 

 interstices being occupied by innumerable spiculse, diverging, 

 and crossing each other in all directions. The whole mass 

 resembles in its texture the white and porous ice, which may be 

 seen at the edge of a pond or small rill where the water has 

 subsided durinp- a frost." 



A variety of hypotheses have been framed with the view of 

 accountingfor this curious phenomenon, all of which, however,. 

 I think I may with confidence assert, are either inadequate to an 

 explanation of the facts, or are altogether inconsistent with the 

 well-established doctrines of chemistry. ' As the point is, there- 

 fore, still open for discussion, I beg leave to state in a very few 

 words in what manner I conceive the deposition to take place. 



While reading Mr. Garnet's paper, I was very forcibly struck 

 with the peculiar circumstances under which he states this 

 incrustation to take place : thus he tells us that ice of this 

 description is seldom seen adhering to any substance, except 

 rock, stone, or gravel ; and that it is always found in greatest 

 abundance in proportion to the magnitude and number of the 

 stones compusing the bed of the river combined with the velo- 

 city of the current ; as also that it abounds most in rough and 

 rapid places, and that he has never observed it where mud or 

 clay is deposited. iVow it has occurred to me that, perhaps, 

 the formation of ice in those situations may be owing to the 

 same causes that give rise to the deposition of dew and hoar 

 frost on grass, Iwigs, and other fibrous substances; namely, by 

 their possessing a greater radiating power, by which they are 

 enabled to discharge a larger quantity of heat from their surface. 

 The roughened surfaces of the stones I conceive to operate in the 

 same way as the vegetable fibres do, in a clear, unclouded atmo- 

 sphere, by allowing each " affluent " wave* to come in closer 

 proximity with the surface, and thus favour the discharge of 

 caloric from the bed of the river. That none appears where 

 mud or earth is deposited, 1 should suppose to be owing to their 

 presenting a comparatively smooth surface, in consequence of 

 which, the stratum of incumbent fluid is prevented coming into 

 such close contact as if a rugged one were presented. Just in 

 the same manner as if we were to take a hiehly polished globe 

 of silver, and fill it with hot water, it will take suppose 20 

 minutes to cool down 10 degrees ; but if its surface be scratched 

 with sand paper in one direction, it will now cool down the same 

 number of degrees in half the time. The striated surface of the 



• Dr, M*Ke€ver adopts Ml|^ Leslie's theory of radiation. — Ed. 



