778 
DR. T. R. ROBINSON ON THE DETERMINATION OE 
this influence proved to be of far greater importance than I had anticipated. On the 
other hand, the vicinity of skilled workmen, ready to make any necessary repairs or 
any alteration suggested by my experiments, was of great importance, and not less so 
the help which Mr. Grubb and his assistant, Mr. Vereker, gave me during the whole 
of this work. 
(2.) The vertical axle of the machine was placed in the centre of the polygon, 
supported by a wooden pyramidal framing. It is an iron tube 3^ inches diameter and 
10 ‘4 feet long. It turns in a collar above and a perforated step below, supported by 
a transverse piece of the frame. On its top is fixed an iron box, 10 inches square and 
12 inches high, open at two opposite sides. The third side supports, on a bar 40 inches 
long, a counterpoise disc of lead, 40 lb. weight, set edgewise. The fourth carries a 
horizontal arm of sheet steel rivetted together, of the section shown in Plate 67, fig. 1 ; 
at the box 5^ inches by 3 inches ; at its outer extremity 2 inches by fths of an inch. In 
this turns the axle of the anemometer between three friction wheels at each end. These 
were at first of bronze, 1 inch diameter, but on May 22 the outer three were changed 
for others of hard steel lyg- inch. On the top of the box is an upright, bearing a steel 
wire attached on one side to the counterpoise, on the other to the arm to prevent its 
flexure. The box also contains a brake apparatus (described at paragraph 21) and 
provision against centrifugal friction. The vertical axis carries near its bottom a 
driving pulley 24 inches in diameter, and both it and the horizontal axis are con- 
nected by circuit interrupt ors with a chronograph. 
The centre of the horizontal axis is 14 feet from the floor, and the plane of the 
anemometer’s arms is 9 ‘0771 feet from the centre of rotation. Hence it follows that 
