Section III., 1897. [ 17 ] Trans. R. S. C. 



II. — On some Measurements of the Temjyeratuî^e of the Lachine Rapids 

 made during the Winter of 1896-97 loith a Differential Platinum 

 Thermometer. 



By IIoAVARD T. Barnes, M.A.Sc. 

 Demonstrator in Physics, McGill University, Montreal. 



(Communicated by Professor H. L. Callendar, M.A., F.R.S., F.R.S.C., 

 and read June 23rd, 1897.) 



In the paper ^ which the writer had the honour to read before this 

 section of the Royal Society a year ago, will be found recorded a series of 

 observations made with new and very delicate apparatus, to deter- 

 mine the extent to which the temperature of the river water opposite 

 Montreal, under the sui-face ice, varied from the freezing point during the 

 winter of 1895-96. 



From these experiments it was shown that the temperature of the 

 river remained exceedingly steady, although the air temperature ranged 

 from — 28° F to + 40° F. Small variations are recorded of a few thou- 

 sandths of a degree, and these were found to accompany atmospheric 

 changes. In no case, however, has a dilference greater than one hun- 

 dredth of a degree from the freezing point been found. 



The writer further pointed out that an elec-trical resistance thermom- 

 eter is really the only form of temperature measuring instrument suitable 

 for work of this jiind, not only because it is capable of greater refinement 

 than can be obtained with any other form of thermometer, but because 

 readings may betaken of the temperature of the river without withdraw- 

 ing the stem from the water. 



The discrepancies in the observations of previous observers have 

 shown that very little reliance can be placed on a mercury thermometer 

 taken out of the water and read in a cold atmosphere. 



Where a large difference below freezing has been obtained by this 

 means, it is important for the observer to state clearly how the measure- 

 ments were taken, and what precautions were used in making the 

 readings. 



In this respect the instrument used in the experiments carried out 

 by Mr. Sproule, the assistant engineer of the harbour commissioners' 

 works, Montreal, on the temperature of the river water, is the most suit- 

 able where an accuracy of not more than 1/lOth of a degree is required. 

 It consists of a mercurial thermometer protected by an outer case, in 

 which a quantity of the water to be measured is entrapped. This serves 

 the purpose of preventing sudden changes in the air. The result of Mr. 

 Sproule's work is found to be in good agreement with that of the writer's, 



1 Transactions of the Royal Society of Canada, Vol. II., Sec. III., p. 37, 1896. 



Sec. III., 1897. 2. 



