116 
DR. P. F. FRANKLAND OR THE QUANTITATIVE ESTIMATION OF 
of the tube pointed towards the wind, the number of organisms deposited in the tube 
was greater than when pointing away from the wind. It is a matter of some surprise 
to me that no reference to this point is made in Hesse’s original paper, and that he 
makes no special recommendation as to the relationship which should exist between 
the direction of the wind and that of the tube. In my experiments with his apparatus 
I have made a practice of directing the open end of the tube at an angle of 135° away 
from the wind, so that the latter does not blow into the tube, whilst, at the same 
time, the experimenter does not intervene between the wind and the open end of the 
tube. The direction of the wind is, however, very rarely so constant that this angle 
can be preserved throughout an entire experiment, which usually extends over 1 hour 
or even more; commonly the direction of the wind is subject to considerable and 
rapid local variations, whilst, sometimes, a complete change of direction takes place, 
in consequence of which I have, in some cases, had to reject the results. In my later 
experiments I have generally exposed side by side with the tube through which the 
air was aspirated a second similar tube by way of control, and I have ascertained 
that the number of colonies making their appearance in the control-tube frequently 
amounts to a large fraction of the number found in the tube through which the air 
has been aspirated. In illustration of this, I may quote the following results obtained 
in this manner :— 
Experiments in Open Air. 
Hesse’s Method with Control-tube. 
I. Gardens of Natural History Museum. June 9tli, 1886. 
12 litres of air yielded. 158 colonies. 
Control-tube. 54 „ 
Wind moderate. 
II. Ditto. June 10th, 1886. 
11 litres of air yielded. 20 colonies. 
Control-tube. 6 ,, 
In this experiment, which was after heavy rain, the wind was very 
slight. 
III. Roof of Science Schools, South Kensington Museum. June 18th, 1886. 
12 litres of air yielded. 12 colonies. 
Control-tube. 3 „ 
Wind slight. 
IY. Ditto. June 22nd, 1886. 
12 litres of air yielded. 53 colonies. 
Control-tube. 11 ,, 
Wind moderately strong. 
