40 THE ROYAL SOCIETY OF CANADA 



Besides the cracks on the upper surface of the ice we observed 

 distinct marks of cracks which had been produced on the underside 

 and which extended roughly only half the thickness of the ice. We 

 could see these cracks through the clear ice on account of the entrance 

 of water into them, with subsequent freezing. From the restricted 

 nature of the freezing, air bubbles were shown eliminated from the 

 water in freezing. Each crack was marked by a thin vertical layer 

 of whitish ice, which showed in contrast to the perfect clearness of 

 the surface sheet. 



Temperature of Water Under the Ice. 



On Feb. 17th, an attempt was made to measure the temperature 

 of the water under the ice. A special mercury thermometer was ob- 

 tained, reading to hundredths of a degree, which was enclosed in a 

 brass protective case with a valve in the bottom. An ice auger was 

 used to drill the ice sheet. This made a clear hole about If inches in 

 diameter, through which the brass case of the thermometer could be 

 readily lowered. The act of lowering the thermometer caused the in- 

 rush of water through the valve of the case, and around the bulb 

 of the thermometer. When held steady, or when raised the valve at 

 once closed, thus trapping the water around the bulb. The thermom- 

 eter could be then raised and the reading taken through a window 

 in the case. The temperatures near the bottom ranged from 3-4°C. 

 to 1 -8°C. A more careful determination of the temperature from the 

 ice surface to the bottom would have been interesting, and a special 

 disc thermometer was constructed for this, but unfortunately the 

 observations were never completed. It is doubtful if they would have 

 yielded anything of importance for this investigation. We may say 

 that the temperature at the underside of the ice was at 0°C. and in- 

 creased rapidly to a probable maximum of 3 •4°C. at the bottom. This 

 is entirely as we should expect from a body of still water upon which 

 ice has formed. 



The disturbance of the water by cutting the hole and lowering 

 the brass case was considerable and owing to this, the readings were 

 variable. 



Thickness of the Ice. 



A series of measurements were made of the thickness of the ice 

 sheet from Feb. 17th to March 14th. This period included some days 

 of mild weather and rain previous to March 5th as well as some periods 

 of intense cold. The mean results we show in Table III and plotted 

 in Fig. 5. 



