352 



Messrs. J. C. McConnel and D. A. Kidd. [June 21 ? 



column gives the temperature just before each, observation, the fourth 

 the actual extension during the interval in millimetres, the error 

 probably not exceeding 0*1 mm., the fifth the rate per hour per length 

 of 10 cm., and the two last the maximum and mean temperatures 

 during the interval. 



On the 10th and 11th the ice broke at the collar, and had to be 

 frozen together again. It will be noted that the rate of extension 

 decreases with the time, more than can be explained by errors of 

 observation, though the tendency of the temperature is to rise. 



Experiment No. 7. Main's Apparatus. — The same piece of ice was 

 used, cut a little shorter (glacier ice C), and fitted with wir& 

 indicators. Only one scale was used for the two indicators, so the 

 readings cannot be trusted beyond 0*5 mm. on the scale. As the 

 multiplication was generally about 16, this gives an error in the 

 actual extensions, when small, not greater than 0'03 mm. When the 

 extensions are large the error is greater, owing to an uncertainty of 

 perhaps 10 per cent, in the multiplication. The "needles" were- 

 glass tubes. The length between the needles was 18 cm., and the 

 area of section 7*3 sq. cm. The first column gives the time of each 

 reading, the second the temperature at that time, the third the 

 interval between two readings, the fourth and fifth the extension 

 shown by the outer and inner indicators, the sixth the mean rate of 

 extension per hour per length of 10 cm., the seventh the tension, the 

 eighth, ninth, and tenth the maximum, minimum, and mean tempe- 

 ratures, during that interval. 



On the 17th February the tension was increased by one-half, and 

 the ice in consequence broke at the collar. It was frozen in again,, 

 and the tension reduced to the original value. On the 8th March an 

 hour was occupied in readjusting the wire indicators. The sixth 

 column shows a rapid decrease of speed for the first five days, 

 followed by fluctuations due apparently mainly to the temperature, 

 the rate at —4° being about double that at —9°. An addition of one- 

 half to the tension increased the rate 500 per cent, for the first two 

 days of the change. This increased rate in its turn showed a 

 tendency to sink, more or less counterbalanced by the rising tempe- 

 rature. The fourth and fifth columns show the curious way in which 

 the more rapid extension alternates from one side to the other. 



This piece of ice, taking the two experiments together, was under 

 tension for twenty-five days, and extended altogether about 6 mm., 

 i.e., about 3 per cent, of its length. At the close of the experiment 

 the divisions between two or three of the crystals at one point of the 

 bar almost amounted to cracks, and at that point there was a decided 

 twist in the bar, estimated at 10°. There were a great many bubbles 

 in the ice, and the crystalline structure was very complex. There 

 was no particularly large crystal. 



