342 



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



wood shavings, except between K and M. Here a wooden partition 

 P was inserted to the left of the vertical connecting rod. The space 

 between K and P was filled with wood shavings. To allow the lever 

 to move freely, it passed through a wooden tube loosely packed with 

 cotton-wool. The outer space between P and M was made fairly 

 air-tight, and the opening through which the lower lever emerged 

 was also plugged with cotton-wool. 



The capacity of the inner chamber was about 60 litres, while the 

 two tins contained about 25 litres of solution. The inner chamber 

 was thus jacketed on all sides with a layer, from 10i to 20 cm. in 

 thickness, of which from 4 to 6 cm. was solid wood and the rest 

 wood shavings. To secure uniformity* of temperature the back of 

 the inner chamber was lined with thick sheet- copper. Originally 

 the front was similarly provided, a small aperture being cut for the 

 cathetometer readings. But after the first experiment this was found 

 very inconvenient and was discarded. Access to the box was obtained 

 from the front, the space between the doors of the two boxes being filled 

 with a movable pad stuffed with shavings. The inner door occupied 

 about half the front of the ice-chamber. With these arrangements 

 the temperature of the interior altered very slowly, often not more 

 than a degreee in 24 hours, though no special precautions were taken 

 to keep the temperature of the room constant. 



We were not so successful in maintaining uniformity of temperature. 

 The minimum thermometer was hung at the back of the chamber 

 on a level with the middle of the ice. The maximum was placed 

 with its bulb at the bottom of the chamber at the end removed from 

 the tin. And we often found that the temperature at the time, shown 

 by the maximum thermometer, was one or one and a half degrees lower 

 than that shown by the minimum. In the temperatures given in the 

 tables allowance is made for this. We found, however, that the 

 variations in the plasticity due to the temperature were far exceeded 

 by others, due probably to changes in the crystalline structure of the 

 ice. In explanation of the considerable variation of temperature 

 occasionally recorded in the tables, we must add that, in order to 

 raise or lower the temperature, the inner chamber was sometimes left 

 wholly or partially open. The front of the box was close by an open 

 window, and was generally exposed to a decidedly lower temperature 

 than the back, so that opening the doors to take the readings would 

 seldom raise the internal temperature materially. 



The bar of ice for an experiment was roughly sawn out and then 

 shaped more carefully with a knife. A hole was bored near each end 

 with a hot steel knitting needle. This was found to be the only 

 method of making a hole free from the risk of splitting the ice. In 

 each hole was frozen a short piece of steel knitting needle with the 

 * Uniformity refers to space, constancy to time. 



