1909 - 10 .] 
Proposal for an Anemometer. 
387 
having its axis in the same direction as, the wind-velocity. It will 
perhaps be more easily understood by reference to the diagram (fig. 1). 
A sphere CDE is mounted on a horizontal axis A' A so as 
to be free to rotate round it. By suitably connecting the sphere 
with a wind-wheel and the horizontal axis with a wind-vane, the 
sphere is caused to spin on the axis at a speed proportional to the 
speed of the wind, while the axis itself veers with the wind so as 
to be always parallel to it, and so that one end of the axis (say A') 
is always at the quarter from which the wind comes. The sphere 
always spins one way (say, right-handedly) as seen from the end of 
A' of the axis ; hence, when the direction of the wind is reversed, the 
rotation of the sphere in space will also be reversed, since the end A' 
W 
will be standing in the opposite quarter. The centre of the sphere 
remains at rest. 
G and K are two small circular plates, horizontal, equal in size, with 
bevelled edges, and free to rotate round vertical axes through the respective 
centres. These plates are brought up below the sphere so as to touch it 
lightly with their bevelled edges. The centre of G is precisely north of 
the centre of the sphere, and the centre of K precisely east ; also they are 
equidistant from the vertical line through the centre of the sphere. Hence 
the plates are on one level, and their points of contact with the sphere are 
at exactly the same distance below the level of the centre of the sphere. 
Under these circumstances, whatever be the direction of the wind, 
the plate G will through its contact with the sphere turn at a speed 
proportional to the north-southerly component of the wind, while the 
plate K will turn at a speed proportional to the east-westerly component. 
Each plate will, of course, reverse its direction of rotation when the 
