22 ROYAL SOCIETY OF CANADA 



To ol»tain any idea of the amount of variation bej'ond 50% of ice, 

 there is requircil more experimental i<no\vle(lge. The dotted rectangle 

 roughly represents the extent of the range during the winter at a point 

 like the Laehine Jiapids, where tlie percentage of ice never reaches a 

 very high ligure. Within this range the author's measurements show the 

 sort of variation to he expected. On Feb. 12th, 1897,' with rapid forma- 

 tion of ice under a strong wind at a temperature of — 2° F. the water 

 showed a temperature 



of _ -OOG") 



and — -0068 

 below the freezing-point. 



On Feb. 7th, under a cloudy sky and air temperature slightly above 

 freezing, the temperature recorded \vas 



+ 0197 



4- -0182 

 This was slightly higher than could be expected, on account of the rain 

 during the day. The effect of the rain was shown the next day, also a 

 cloudy, rain}' day. when the temperature reached 



+ -0547 

 + 0415 



During this time the ice was very thoroughly cleared out of the rapids. 

 On the other days, with a bright sun, the temperatures measured were 

 effected by the absorption of the solar heat in the water. 



To fix the freezing-point of water for accurate temperature measure- 

 ments, it is necessary to define the quantity of ice and water and the 

 rate of loss or gain in heat to the surroundings. With an even mixture 

 it is not certain whether the two branches of the curve for a gain or loss 

 of heat will meet, or whether they will still be separated by a minute 

 temperature difference. It is probable they will be, and in that case a 

 freezing-point mixture must be defined as an intimate and equal mix- 

 ture of ice and water, neither gaining nor losing heat. 



The above considerations must be supported by laboratory experi- 

 ments before conclusive figures can be deduced, and especially in the 

 region beyond the dotted line. The dotted region may be considered to 

 be fairly well substantiated by existing data. 



' Second conimunicfttlon, p. 22. 



