Sl06 Mr. Ferguson on the Cause of the Holes 



As none of the circumstances attending the formation of ice 

 seemed to account for the appearance of the holes in question, 

 attention was next given to ice during the process of melting. 

 After the formation of ice, indeed, and while hard frost con- 

 tinued, nothing rudimental of a hole could ever be observed. 

 Thus the question came to be. What circumstance in the 

 melting gave rise to the holes ? 



Their frequent occurrence in ice at the mouths of rivers 

 might suggest the idea of their being dependent on salt water 

 — a conjecture supported by the well-known effect of salt in 

 lowering the freezing point of water, and its consequent power 

 of melting ice. The holes, however, occur in inland pools, 

 and in rivers at a distance of several miles from the sea. I 

 froze sea-water by exposing it during a very cold night to ra- 

 diation — the natural freezing agent. When the ice thus pro- 

 duced was melted, in almost every natural manner, none of 

 the holes were formed, but only a spongy porous texture, in 

 consequence of the rapid melting apart of almost all the ice 

 impregnated with saline substances. I also immersed com- 

 mon ice in sea- water, where the melting took place more ra- 

 pidly than in fresh of the same temperature ; but, in other 

 respects, little, if any, differenceof action was observed. From 

 these and similar considerations, I inferred that the formation 

 of the round holes is little dependent on the presence of saline 

 substances in considerable quantity — much less in the ex- 

 ceedingly minute quantities held in solution in ordinary fresh 

 water. 



The remarkable property of becoming specifically heavier, 

 as it ascends in temperature from 32° F. to 38° F. belongs to 

 water. On account of this property, water lying in a depres- 

 sion on the surface of a sheet of melting ice, would obviously 

 undergo a circulation, the portion heated by the air descend- 

 ing in the centre, and, when cooled by ice at the bottom, 

 rising by the sides. The immediate consequence of the warmer 

 water being thus always conveyed to the bottom, would be to 

 melt the ice at that part, and thus produce a hole. But when 

 a depression was made in a sheet of ice, and water put into it, 

 the depression, so far as I could observe, continued of the 

 same depth during the whole time of melting. Hence, in such 

 circumstances, the ice probably received the heat as fast as the 

 water. 



After having thus far failed to account for the appearance 

 in question, I made an observation that indicated what seems 

 to be the real cause. 



In the course of my observations on ice melting on the 

 sides of rivers, I frequently saw holes not entirely perforated 



