SOME REMAEKS ON 
205 
pressure on x square feet may be. Since in a storm the wind 
scarcely ever blows steadily, the velocity of wind during a gust 
and its duration appear, therefore, to be the quantities which 
it is most desirable to determine. About the same time that 
Mr. Osier invented his pressure anemometer. Dr. Whewell 
invented another which measured the velocity of the wind. This 
instrument, which has been described elsewhere,^ had several 
serious objections, and as both Prof. Airy and Sir W, Snow 
Harris concluded, could not be depended upon as giving accurate 
results, and its use was ultimately abandoned. Nevertheless its 
construction marks an epoch in the history of anemometers, since 
it was undoubtedly the first instrument of its kind, - and the 
results obtained from it were of considerable interest. The 
essential portion of the instruments which have entirely super- 
seded it was first employed by Dr. Robinson about the year 
1845. This portion is the head of the instrument, and consists 
of a number of hemispherical cups (generally four) so arranged 
about the vertical spindle as to cause the wind to turn it always 
in one direction. Inasmuch as the only essential difference 
between the various velocity anemometers in use is the mode of 
indicating or recording the revolutions of these cups, it was 
therefore a matter of great importance to determine the ratio of 
their velocity to that of the wind. Dr. Robinson’s first investi- 
gations led him to conclude that 
V = 3v. 
when V" and v are respectively equal to the velocity of the wind 
and cups ; but this relation, after being universally accepted for 
many years, was shewm by the Rev. F. N. Stow and M. Dohrandt 
to be far from correct, and later investigations of Dr. Robinson 
also confirm the fact that except at high velocities there is no such 
direct relation between V and v. The latter gentleman has, by 
^ Camb. Trans., Vol. IV.; and Brit. Assoc. Report, Vols. IX., X. 
