18 ROYAL SOCIETY OF CANADA 



ahout two i)arls in oik* thousand. The mean values are given by Nichols' : 



For artificial ice, U'HH)! 

 For natural ice, 09 ISO 



Another interesting point brought out by Nichols's experiments is 

 that, from certain of his preliminary results, ice formed at a low 

 temperature is denser than ice formed at a higher temperature. He 

 remarks, however, that '-the whole question of the influence of time, 

 and of the condition under which freezing occurs, is one which demands 

 further and more extended investigation." It occurs to the author that 

 possibly the phenomenon noted during an extremely cold day, of the fine 

 frazil crystals apparently floating lower in the water than during milder 

 weather, might be explained by the fact of their very rapid formation 

 at a low temperature. Such ice, as Nichols observes from his experi- 

 ments, would tend to pass back to the normal density with lapse of time. 

 Fi'om Nichols's work it appears that the greatest density noted was one 

 part in one thousand higher than normal, so that this would have very 

 little appreciable efiect on the buoyancy of the ice. Whether the tine 

 crystals formed as frazil crystals are would under extremely rapid growth 

 have a greater density than that found by Nichols, must be settled by 

 further experiment. It is a possible explanation of this well known 

 phenomenon, and when coui)led. vvith the fact that the water is very 

 slightly undercooled, which would render it less dense, it assumes a more 

 plausible aspect. 



Sec. II. O.v Radiation as the Cause op Anchor Ice Formation. 



It has been suggested th::t further experiments are required to settle 

 the question of the efiect of radiation in the formation of anchor ice. It 

 ai)pears to the wi'iter, after a careful consideration of the data available, 

 that the primary cause of the formation of ground ice is radiation. It 

 has been urged, however, in the writer's experiments to determine the 

 depth of penetration of the sun's raym,' that if at two feet immersion of 

 the thermometer bulb the temperature indicated had fallen oflf so much 

 compared with eight inches immersion, then at only a few feet would 

 the etlbct become extinct altogether, whereas it is known that anchor ice 

 forms at depths varying from 30 to 40 feet. It must be borne in mind 

 that a linear relation may not be assumed to connect the distance with 

 the amount of penetration. It is evident that the greatest absorption 

 takes place in the first few feet of water incapable of transmitting the 

 thermal rays of great wave length, after which the absorption falls off 

 more and more as there is left in the penetrating solar ray the light 

 waves of small wave length, and the thermal waves approaching more 



' Loc. cit., p. 36. 



* Second communication, p. 2-1. * 



