146 ROYAL SOCIETY OF CANADA 



temporary spell of mild weather frazil will form again upon the return 

 of cold weather — in the same manner as it does in the early part of 

 almost every winter. 



One of the many remarkable properties of water is that it is lighter 

 when its temperature is just at the freezing point than when its tem- 

 perature is at any other point within 7 degrees of the freezing point. 

 This peculiarity is illustrated in Fig. la in which layers of water at 

 various temperatures would take up the respective positions shown. Ice 

 floats on water and it may be noted also that water at the freezing point 

 would rise to or stay at the surface and form a protective covering for 

 the main body of water if the surface were left undisturbed. The condi- 

 tions illustrated in Fig. la, however, are not usually allowed to obtain — 

 they are upset by the boisterous winter wind, by rough rapids and by the 

 greedy power users wlio are rarely content to let the water flow along 

 towards their water wheels in a smooth quiet manner. 



The Ottawa District has become famous, amongst the engineering 

 profession, as a frazil-manufacturing centre. Why it has achieved this 

 reputation may be learned by a study of that portion of the Ottawa 

 River — Fig. 1 — from which most of the energy used in the district 

 comes. 



The hydraulic power plants in this vicinity are nearly all situated 

 at the Chaudière Falls at Ottawa and Hull. As may be seen in Fig. 1 

 these power plants are below three sets of rapids. There are also a few 

 power plants at Deschenes — just at the Deschenes Eapids. 



Your attention is specially directed to the fact that the Deschenes 

 plants, although having no rapids or water-falls above them, for 25 

 miles, are placed Jiors de combat almost every winter by frazil. This is 

 explained as follows: 



'A cold northwest wind is the harbinger of winter. This wind, 

 crossing it as it does, lashes and furrows Lake Deschenes and prevents 

 sheet-ice from forming on its surface. A tremendous amount of frazil — 

 the ice spicules which would soon unite and become sheet-ice but for the 

 disturbing action of the wind — is manufactured in Lake Deschenes itself 

 before the rapids are reached at all ! The sides and the bottom of the 

 outlet of Lake Deschenes are so rough in character that the velocity of 

 flow at the surface is perhaps greater than at any other portion of the 

 stream. On account of this great surf ace- velocity much of the frazil 

 formed on the surface of the lake is drained through its mouth and into 

 the power plants. The water in the rapids is of course kneaded — 

 as a baker kneads dough — from top to bottom and bottom to top and new 

 water surfaces are being continually turned up and subjected to the cool- 

 ing action of the air. The temperature of the water at this rapid, in- 



