so ROYAL SOCIETY OF CANADA 



the Montreal Flood Commission, illustrate this, and show how the area of 

 ice gradually diminishes and the area of free waterwaj^s gradually in- 

 creases as the sections recede from the rapids. 



The formation of anchor ice obviously cannot take place under any 

 surface which would act as a check to radiation, such as an opaque layer 

 of surface ice. Tbere is another important reason why, in very deep 

 water, anchor ice is not readily formed. Below 4° C. warmer layers of 

 water sink to the bottom, and colder layers rise. The bottom of a deep 

 river not flowing with sufficient rapidity to cause a thorough stirring, 

 may well be above freezing. Whenever, also, water is flowing so slowly 

 as to prevent agitation, a surface layer of ice generally forms, and further 

 prevents the growth of ground ice. A thick mass of water also acts as a 

 resistance to radiation, especially if the water is not perfectly clear. 



A great deal more might be said in regard to the formation of river 

 ice, but as the writer has already written fully on this subject in an article 

 published in the Canadian Engineer for May, 1897, it becomes the less 

 necessary here. Again, the present paper is intended more as a sequel 

 to the writer's first paper, in which will be found a full discussion of the 

 "principal points brought out by previous observers. 



In conclusion, the writer desires to call attention to the report of 

 the Montreal Flood Commission, which tras recently come under his notice, 

 as deserving of the highest praise. The untiring efforts of the engineers 

 on the Commission, during so many years of tedious and necessarily severe 

 work, in collecting d ita for the charts and diagrams accompanying the 

 report, make it of inestimable value. 



The writer also desires here to acknowledge the kind encouragement 

 and generous aid in carrying out the present series of experiments so 

 willingly given by Professor Calleudar and Mr. John Kennedy, as well as 

 to express his thanks to the Lachine Hydraulic Co. and the many promi- 

 nent engineers who have taken an interest in the work. 



