68 ROYAL SOCIETY OF CANADA 



The worst efEects which are met with in engineering works are 

 from frazil crystals formed during extreme weather when anchor-ice 

 ir. growing rapidly hy the freezing down of the crystals and not, as 

 is sometimes supposed, when moderate weather occurs and these huge 

 Jumps become loose and rise to the surface. Thus, it is often thought 

 that it is useless distinguishing frazil from anchor ice unless it were 

 possible to tell them apart at the foot of a stretch of open water 

 where they accumulate at the edge of the barrier ice. They are cer- 

 tainly both ice; but the conditions under which anchor ice will form 

 are not the same as for frazil and vice versa. Methods of construction 

 to obviate the one will not meet the exigencies of the other. So long 

 as the ice problem lasts we shall find circumstances conducive to the 

 formation of either one or the other or both. We should, therefore, 

 keep clearly in our mind how each is likely to be formed in order 

 to be prepared to distinguish the conditions most likely to favour the 

 growth of either. In a shallow, smooth flowing river, we are more 

 likely to have anchor-ice formed in excess, whereas in a deep and 

 turbulent stream we are likely to have more frazil. It is hardly likely, 

 however, that there will be a great difference in the amount of frazil 

 formed; it will probably be that more ot less anchor-ice will appear 

 in proportion. In a river 40 or 50 feet deep anchor-ice is almost 

 unknown, although large quantities of frazil are met with. 



Everything seems to point to radiation as the prime cause of 

 anchor-ice, and it is a great question whether it would form at all, 

 or except in exposed or exceedingly shallow rapids unless the first 

 coating of ice was placed over the rocks by the radiation of heat. 



Consider the circumstances : the water flowing over the rocks at 

 the bottom of a river is always very close to the freezing point. The 

 deviations from the freezing point, as I have shown elsewhere 

 in these Transactions (1896, 1897), are seldom as great as 1/100° 

 Falir. The bottom is continually being warmed to a small amount 

 by the conduction of heat from the earth. It is therefore dif- 

 ficult to see how ice can form on it by heat loss directly to 

 the water. The utmost frost that can be present is only 1-100 of a 

 degree, which would form but a minute layer. Unlike open ground 

 subjected to extremely cold air, the bed of a river cannot become frozen 

 to any extent unless in very shallow streams. 



The radiation of heat from the bed of a river must go on all the 

 time to the colder air above and to the much colder space. During 

 the daytime, under a clear sky, we have the sun's heat radiated down 

 through the water and offsetting the cooling effect produced by the 

 space radiation, and on a cloudy day, we have the heat rays reflected 



