18 ROYAL SOCIETY OF CANADA 



in 80 far as it shows, within the hmits of accuracy of his readings, that 

 the temperature of the river water never varied from the freezing point 

 throughout the winter, either under the surface ice or in open water. 



In the charts of air and river temperatures now in the possession of 

 Mr. John Kennedy, made by the late Mr. T. D. King for the Grand 

 Trunk Eailway at Victoria Bridge, will be found recorded variations in 

 the temperature of the river water, under the surface ice, amounting to 

 several degrees either way from the freezing point. Unfortunately, it is 

 not known definitely to the writer how the observations Avere made, or 

 what precautions were taken against sudden changes in the air. As the 

 variations do not correspond, however, with changes in the temperature 

 of the air, they suggest possible errors of observation. 



The purpose of the present paper is to record a number of observa- 

 tions made by the writer during the past winter of the temperature of the 

 Lachine rapids, in continuation of the measurements, already described, 

 made under the surface ice at the guard pier opposite Montreal. 



It was considered almost certain à priori that the temperature of the 

 open water in the Lachine rapids could not differ to any large extent from 

 the freezing-point. But, as a matter of further interest, it was deemed im- 

 portant to establish this by direct experiment, and to determine, as far as 

 possible, the relationship between the formation of frazil ice and the tem- 

 perature of the water. 



Place of Observation. 



It was difficult to choose a place for making the measurements which 

 would present a sufficient variety of conditions in the state of agitation 

 of the water, to enable the readings to be of value in determining any 

 inequality in temperature throughout the mass of the river. 



The first locality selected was at the foot of the rapids, between the 

 north shore of the river and He Héron, at the spot where the main cur- 

 rent runs under the barrier ice. It was soon seen, however, that this 

 would prove to be a most dangerous place in which to leave the obser- 

 vation shanty and instruments, on account of the continually shifting 

 surface ice. A shove of considerable size might at any moment take 

 place here during extreme cold weather, owing to the complete blockage 

 of the channels under the ice by frazil. A place was finally selected 

 higher up, which from the solidity of its foundation, and the character of 

 the water in the immediate vicinity, made it as suitable as could well be 

 desired. 



The Lachine Hydraulic Co., their works being then under construc- 

 tion, had built out from the north shore, for a considerable distance, a cof- 

 fer-dam of earth and stone, which, with the outer dam of the same material, 

 extending down to the power-house, served to turn aside an immense 

 volume of water, otherwise to be employed for power purposes. Just at 



