2o8 
James Small. 
hook F. The whole apparatus then acts as a simple mechanical 
couple. The hook F is the same distance from the fulcrum G as 
the top of the T beam, so that the weight on the scale pan and the 
weight of the thread, together with that of the scale pan itself, 
give a direct measure of the total pressure on the disc A. The 
pulley M has practically no friction, being a small brass wheel 
running on steel needle points. These needles N and O are 
adjustable, and when in proper condition the wheel runs for quite 
half a minute with no sound when given a slight touch. This 
practically frictionless pulley and the axis at G, which is balanced 
on sharp agate edges, are the only two points at which friction 
might cause an error. 
When in use with the tube the disc of the anemometer was 
inserted a short distance into the tube, and as the diameter of the 
disc is 3'3 cms., and that of the tube is 4‘5 cins., the conditions 
were very similar to those under which the fruits were acted upon 
by the wind. The almost complete absence of friction and the 
accuracy of the instrument are both proved by the fact that in a 
wind sufficient to balance the weight of the scale pan and thread 
the placing of a weight of '01 gms. on the scale pan brings the beam 
as far out of the vertical as the construction of the stand will allow. 
An accuracy of -001 gms. is certainly not too much to claim for 
the instrument. 
The smallest weight which it is possible to use is ’16 gms., 
this being the weight of the scale pan and its suspending thread. 
Structure and Properties of the Wind Used. 
The strength of the wind produced by the fan varied with 
the four speeds as above mentioned, and the strength of the wind 
entering the tube could be controlled further by moving the tube 
away from or towards the fan. The tube was kept carefully aligned 
with the centre of the fan. 
Smoke was passed through the tube and no marked rotatory 
movement was observed; the smoke passed straight through, never 
twisting through an angle of more tha*n 90°. Close to the inside 
surface of the tube it was retarded and continued to come out for 
some time after the central mass had passed. The region of 
retardation was very narrow compared with the width of the tube. 
It is clear, therefore, that the wind is more or less horizontal with 
a straight movement through the tube. 
The structure of the wind was further investigated by means 
