138 Proceedings of Royal Society of Edinburgh. [sess. 
stage, interfered with the correctness of the results. After this another 
plan was tried, and it has been found to work satisfactorily. It con- 
sists in reducing the height of the receiver as much as possible, and 
increasing the horizontal dimensions to such an extent that the verti- 
cal currents do not move across the receiver and disturb the air over 
the counting stage ; in addition to this, the stage is placed on a floor 
in the receiver, because when supported at a height, as in the first 
receiver, currents are formed on the support and rise round it, 
disturbing the air, and interfering with the equal distribution of 
the drops. The new arrangement gives most satisfactory results. 
When expansion is made, the condensed particles are seen falling 
vertically, and the distribution of the particles is even all over the 
stage, which would not be the case unless there was an entire absence 
of currents while the drops were falling. 
The manner in which this plan has been practically carried out 
will be best understood by a reference to Plate II., where fig. 1 is 
a vertical section of the receiver ; fig. 2 is another vertical section at 
right angles to fig. 1 ; fig. 3 is a horizontal section, while fig. 4 is a 
plan of the top of the receiver. A is a glass cylinder, such as is used 
for pneumatic experiments, with its ends melted and ground. B is 
a circular disc of plate glass, ground and polished, which closes the 
upper end of the cylinder A. The bottom of the cylinder is closed 
by the metal disc C, through which pass the different tubes pre- 
sently to be referred to. The bottom may be cemented to the 
cylinder, or a ground joint may be employed. The counting stage E 
is supported inside the receiver by means of the tube D — the 
upper surface of the stage being at a distance of exactly 1 cm. from 
the glass top B. The tube I) is supported inside the receiver, and 
kept vertically in its place by means of the tube F, which is part of 
the metal bottom C, or fixed firmly to it. The tube D has a shoulder - 
piece G worked on it in such a position that when D is in its place, 
and the shoulder G pushed up into contact with the lower end of E, 
the counting stage is in its correct position, namely, 1 cm. below 
the glass cover. H is a piece of indiarubber tubing, to prevent air 
entering between D and F. I is a thin disc of metal slightly smaller 
than the inside of the receiver, and pierced with three holes to allow 
tubes to pass through it. The diaphragm I is used as a false bottom 
and as a stirrer for mixing the air in the receiver. K is a short 
