[BARNES] TEMPERATURE OF THE LA CHINE RAPIDS 23 



of the maximum and minimum air temperatures were measured at the 

 rapids with a suitable registering thermometer. The column^of differ- 

 ences contains temperatures for both the swift current and quiet back 

 water.. 



It will be seen that during the warm, rainy weather, the current was 

 a little warmer than the quiet water, while during the clear weather, with 

 a large percentage of sunshine, the current was colder. These readings 

 were all taken during the day and show what an enormous influence 

 the sun has in warming the water, although the air temperature remained 

 cold. The wind has a marked influence in cooling the water,"especially 

 if it is blowing against the current, as on Fcl>. 12th. On this date the 

 largest difference below freezing was recorded. It is interesting, fi-om 

 purely theoretical considerations, to see that the water, being vigorously 

 churned and mixed with air, showed an indication of being warmer than 

 the quiet water. Immense quantities of ice were manufactured on this 

 date throughout the mass of the river, giving a general brown, sandy 

 colour to the water, more especially in the swifter currents. 



A shallow portion of the current near the shanty gave excellent 

 opportunity for studying the growth of ground ice. When the tempera- 

 ture observations were commenced on February 3rd, large masses of anchor 

 ice were located there. These were disintegrated and otherwise com- 

 pletely cleared away during the warm, rainy weather from February 6th 

 to 9th. On the nights of Febi'uary 10th and 11th anchor ice appeared 

 again growing in situ and in greater abundance on the darker rocks. 

 On February 12th, owing to the slight undercooled state of the water, 

 floating ice carried down by the currents stuck in quantities to thegi'ound 

 ice, causing it to grow to a great thickness. Large islands of ice appeared 

 also scattered through the rapids in the shallower parts. On February 

 13th, although the air temperature still remained cold, the bright sun 

 served to warm the water and to bring up a great deal of ice. The river 

 was of an entirely ditibrent colour, and there was apparently no ice form- 

 ing in the water beyond a small amount of fine ice in the currents pro- 

 duced by extreme agitation. Early in the morning there were also no 

 blocks of anchor ice visible, but as the sun became stronger, immense 

 quantities of this ground ice were brought up and floated down. During 

 the remaining time of the experiments there was a continual formation 

 of ice on the bottom near the shanty, on the cold, clear nights, and a cor- 

 responding melting, by the heat of the sun's rays peneti-ating the water 

 during the days following. 



In order to test the effect of radiation in the water, both during the 

 day and night, some readings were taken on February 13th, 15th, and 

 26th. On February 13th and 15th the readings were taken at noon, 

 with the sun at its brightest, in the quiet water just over the edge of some 

 bordage ice formed out from the pier. By this means the stem of the 



