206 
James Small. 
attached to a small motor B ; by means of different resistances 
the speed of the fan could be varied. In the results given below 
Speed 1 is the slowest and Speed 4 the fastest. A wooden guard 
P, covered on one side with a net, surrounded the fan. 
The fruits were blown through a glass tube C. As it was 
found that the wind eddied at the near end of the tube, a hole D, 
2 cms. long and 1 cm. wide, was cut in the tube at a distance of 
5 cms. from the end; through this hole fruits were dropped. As 
the whole length of the tube was 132 cms., this gave 125 cms. as 
the length for dispersal. A two-meter rule E was used, but as it 
was placed against the net 3‘5 cms. were added to the readings to 
get the distance from the boss of the fan. This accounts for the 
constant occurrence of this number in the figures given below. 
Anemometer .—The wind pressure was measured by means of 
an anemometer designed for the purpose. The ordinary rotating 
anemometer is empirical and not accurate for slow speeds (cp. 7), 
and further it was more important to obtain a measure of the pres¬ 
sure of the wind on a surface somewhat similar to that of the 
pappus than to obtain an empirical measure of the velocity of the 
air moving through the tube. 
The anemometer (see Fig. 26) consists of a thin circular disc 
of tin A against which the wind impinges. The disc is accurately 
balanced by a ball of solder B on the other end of the top of the T 
beam. The horizontal part C of the beam is a thin steel rod, 
soldered to a flat strip of tin which forms the vertical part D of 
the T. At the base of D are a needle indicator E and a small 
hook F. The whole of the T beam is accurately balanced by 
means of solder on the back of D, so that when balanced on the 
watch-wheel fixed to D at G it remains in any position in which it 
is placed. In the instrument this T beam is balanced by the steel 
axis of the watch-wheel on adjustable agate edges at H and K. It 
is therefore free to move in any direction with a negligble friction 
when acted upon by a small force. 
