36 Joty—On the Conservation of Mass. 
The scale beg also north and south, the south end of the scale is distinguished 
by numbers in italics, the north end by ordinary type. Thus if the numbers in 
italics are diminishing, the light-spot is moving from the south end of the scale 
towards the centre, and consequently the vessels are travelling westward. The 
same direction of motion prevails if the numbers in ordinary type are increasing. 
On the other hand, the motion of the vessels is easterly if the ordinary numbers 
are diminishing, the figures in italics increasing. The results are plotted so far 
as is consistent with reasonable economy of space. In the curves upwards is 
equivalent to easterly, and downwards to westerly motion of the vessels. The 
full horizontal line indicates the zero of the scale, and from this the scale 
divisions are laid off vertically, 20 scale-divisions to 1 centimetre. 
The intersection of the curve with each ordinate is a point fixed by a reading 
of the position of the light-spot on the scale. The ordinates are uniformly fifteen 
seconds of time apart, the observations being made at this time-interval. 
EXPERIMENTS. 
Experiment on the Conductivity of Heat through the Jacket of Cork-dust, 
A glass bulb of about the size and thinness of the lower bulb used in the 
experiments, containing 27 ces. of water, at a temperature of 16°60, and closed by 
a cork through which passes the stem of a sensitive thermometer, is placed in the 
paper cylinder, and surrounded by the jacket of cork-dust just as in the experi- 
ments to be described. The whole occupies the usual position in the zinc-lined 
box. A second thermometer placed in the box gives the temperature of the air 
within the box. The times of observation beginning at 0 minutes, and the 
thermometer readings corresponding in the cooling water 7’, and in the air 7, were 
observed as follows :— 
O minutes 7 16°60, ¢ 12°:80. 
AQ) TE 15°35, ¢ 12°°65. 
(Hop T 14°80, ¢ 12°-69. 
90a TVS AO Eee 68% 
US ap F 14°10; ¢ 12°°62- 
140K Fass TE ISSO, B UOT. 
UGH 9 T 18°58, ¢ 12°°54. 
195 op T 18°32, ¢ 12°-50. 
22.0 ens 4M TBO), GB Up oeks}, 
If these results are plotted, it will be found that when the steady state is reached, 
and with a difference of temperature of 1:2 degrees, the fall is at the rate of one 
degree in 11°7 minutes. Taking the water equivalent of the glass bulb (15 grms.), 
and of the thermometer bulb together as 3 grms., we find that 30 calories pass 
