700 J. B. HANNAY ON A METHOD OF DETERMINING 
cool before breaking if high temperatures were used ; so the apparatus in fig. 
1 was used for temperature work, and that in fig. 2 for rate work. This 
apparatus has a pen at A, attached to which is a little tray, and both are held 

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2 
mi SS 
Fig. 2. 
at the end of a spring B, which is twisted at right angles at the middle, so that 
it is both a vertical and horizontal spring. It is fixed, pressing against the 
cylinder C, and when the latter is rotated it draws a straight line round the 
paper coiled on the drum; but when a drop falls on the tray it bends the 
spring and makes a depression in the line, and by the number of depressions 
the number of drops is registered. Each drop, after striking the tray, falls into 
the little basin placed below. The rate of rotation is regulated by the fly D, 
which can be regulated to any resistance. With these two apparatus the 
investigation can be carried on with great ease and certainty, the only disturbing 
cause left being that when quick rates are used, the breaking of the neck com- 
municates a vibratory motion to the forming drop, which slightly affects its size 
at different rates. The following table gives the numbers obtained while experi- 
menting with mercury at the ordinary temperature :— 

