[barnesJ temperature OF THE LACHINE RAPIDS 29" 



The nij's of the sun, which have already been shown to have such an 

 important influence in determining the temperature of the river water, 

 also have a powerful effect on the growth of ground ice. Under a bright 

 sun, anchor ice cannot form. The solar heat is radiated through the 

 atmosphere and water, and by passing directly through the anchor ice 

 itself to the bottom, melts off its hold. 



The writer has fiequently noticed, during the progress of these ex- 

 periments, that in the early morning, after a cold, clear night, there was 

 little floating ice visible be3'ond the usual amount of fine ice in the 

 currents. As soon, ho\<^ever, as the sun rose higher and became more 

 powerful, the surface of the river was dotted over with the characteiistic- 

 white patches of atichor ice. Immense quantities were thus brought up 

 from the bottom and floated down. 



In regard to the specific gravit}' of subaqueous ice, the best proof of 

 the fallacy that ice, on account of its density, is ]3revented from rising, as- 

 stated by some observers, is in the way in which anchor ice forms. It is 

 well known how it grows in long needles as far as possible in a veitical 

 direction, taking beautiful atborescent forms. This shows a tendenc}^, on 

 the part of the ice, to be buoyed up even as it is made. The branching 

 condition of ground ice would also help to entangle and collect the fine 

 floating ice crystals. The force tending to raise the mass is often suf- 

 ficient to tear it awaj^ from its foundation, and, as is well known, lift 

 stones of considerable size. 



There is very little doubt that the greatest amount of the fine fl ating 

 ice found in our rivers is due to surface agitation cav;sed by current or wind. 

 The more water is being churned up and mixed with air, whereby its ex- 

 jjosed surface is increased, the faster will be the abstraction of heat, and 

 the greater the quantity of frazil formed. During extreme cold weather,, 

 especially with a high wind or with a great deal of radiation at night, the 

 mass of the river is thrown into a very slightly undercooled state. The 

 adhesiveness of the ice was noticed by the wiiteronly when the water 

 was in this state, and could in general be easily anticipated from atmos- 

 pheric conditions. In this state the worst effects from fi-azil are to be- 

 met with due to its agglomerating. While measurements were being 

 made of the temperature of the water on February r2th, when it was. 

 slightly undercooled, the thermometer stem was placed in the current 

 just resting on the surface of some ground ice. It soon became frozen 

 down, and could only be removed with great difficulty without injury. 



Under surface ice, of course, frazil cacnot form, but wherever an open 

 stretch of water occurs, immense quantities are swept under the barrier 

 ice and carried into quiet waters, there to rise and become attached to the 

 under side of the surface sheet. This goes on during the entire winter,, 

 until, for miles below the Lachine Eapids, the surface ice is solid in many 

 places to the very bottom. Cross sections made of the river, jDublished by 



