1912] on Iceharffs and their Location in Navigation. 



531 



The Recording Micro-thermometer. 



The development of the recording micro-thermometer has been 

 the result of nearly twenty years' experience in the study of minute 

 temperature changes in the ice-bearing water of the St. Lawrence 

 river. By applying very sensitive electrical resistance thermometers, 

 it has been possible to show that the temperature of the St. Lawrence 

 in winter never varies more than a minute fraction of a degree from 

 the freezing point. The small variations that have been observed 

 and measured are the result of heat exchanges when ice is present, 

 and they accompany the formation or the disintegration of the ice. 

 The delicate jwising of the forces of Nature are here wonderfully 

 illustrated. A few thousandths of a degree on either side of the 

 freezing point of the river water produces immense physical effects. 

 Thus the character of a river may be changed in a single night, or 

 the wheels of the largest hydro-electric station completely stopped by 



Fig. 2.— Bulb of Micro-thermometer. 



a drop of a few thousandths of a degree in the temperature of the 

 water. As a result of this knowledge^it is now possible to apply arti- 

 ficial heat around the wheels and gates, and completely prevent any 

 trouble from the sticking of the ice needles drawn in by the water. 



Four years ago I undertook some experiments to study the ice- 

 breaking operations on the St. Lawrence, and to determine the effect 

 of open water conditions on the temperature of the river. During 

 this time I turned my attention to a practical form of electrical 

 resistance thermometer, which could not only easily measure thou- 

 sandths of a degree but automatically record them on a chart when 

 working from the ice-breakers going at full speed. Following out 

 ideas which I had developed along these lines, I devised an instru- 

 ment which has proved so satisfactory and trustworthy that I have 

 given it the name of the micro-thermometer. 



The thermometer bulb. Fig. 2, consists of concentric cylinders of 

 Vol. XX. (No. 106) 2 n 



