TRANSACTIONS OF SECTION A. 731 
equivalent to a resultant duct whose equivalent orifice is equal to the sum of the 
equivalent orifices of the components. 
These Laws are applied to furnish solutions (making certain assumptions) to the 
following problems :— 
1. To determine from measurements of the flow the equivalent orifice of a 
duct—e.g., a chimney. 
2. To determine the equivalent orifice of the casual inlets (chinks in doors and 
windows) of a room. 
3. To calculate the amount of air that will enter by an open window into an 
otherwise closed room, maintained at a known difference of temperature above 
that of the outside air. 
4, To calculate the conditions under which a straight vertical chimney is liable 
to act as inlet and outlet simultaneously. 
5. To calculate the condition under which the outward flow through an extract- 
ventilator is liable to be reversed in a room with an open fire. 
6. To determine the conditions necessary for the isolation of one circulation 
from another—e.g., to prevent the air of one room passing into an adjoining room. 
9. Account of Hzperiments to determine the Variations in Size of Drops 
with the Interval between the Fall of each. By W. Binnie, B.A. 
These experiments were carried out while the author was engaged in construct- 
ing a self-registering rain-gauge, designed so as to count each drop as it fell from 
the funnel. Thus, the correct working of the gauge depended on the assumption 
_ that drops falling from a tube remained constant in size under varying conditions. 
This assumption proved partially incorrect, as it was found that the size of the drops 
varied, within certain limits, with the interval of time between the fall of each; 
_ but, as will be seen, by choosing the funnel of such a diameter as not to discharge 
drops at more than a certain speed, error from this cause could be eliminated. The 
variations which took place with various tubes of different diameter, also with a 
drop falling from a plate, were shown in a diagram; the horizontal scale re- 
presenting the interval in seconds, the vertical the size of drops in hundredths 
of one cubic centimetre. Similar variations took place in all the tubes. When the 
interval remained constant, the size of the drop was constant. When the interval 
between the fall of each drop was greater than ten seconds or thereabouts the size 
of the drop became constant, as shown by the curve in each case becoming parallel 
with the horizontal scale. About this point a variation began to set in when the 
intervals between the fall of each drop grew shorter, and this variation rapidly 
increased, until, when the interval became nothing, or, in other words, the drops 
formed a stream, a drop of infinite size, the curves would become asymptotic to 
the vertical scale line. The curves show the variations which take place between 
these two extreme cases. Drawings of the drops seemed to indicate that, with 
intervals shorter than ten seconds or thereabouts, small accessory drops became 
split off together with one main drop, so that the variation might be due to the 
fact that this accessory detachment became larger relatively to the main drop as 
the interval became shorter. The theoretical size of the drop for each tube is also 
plotted on the diagram, and is in each case considerably above the value of the drop 
when it became constant. This might be due to the tubes not being perfectly 
clean. 
FRIDAY, SEPTEMBER 65. 
The following Papers were read :— 
1. Recent Determinations of the Absolute Resistance of Mercury. 
By R. T. Guazesroor, M.A., F.R.S. 
