[ 212 j 



XXIII. An Integrating Anemometer. By Walter Bailt*. 



[Plate V.] 



THE object of the instrument described in this paper is to 

 resolve the velocity of the wind in two directions at 

 right angles to one another, and to obtain the time-integral of 

 each part separately. 



The instrument contains a horizontal plane, in which are 

 two slits X S and E TV, forming a cross to be placed with its 

 arms towards the cardinal points. In these slits are sliders 

 F, G, connected by a bar of constant length. Ois the centre 

 of the cross, H the centre of the bar. The locus of H is a 

 circle with centre 0. A weathercock or some equivalent 

 mechanism is to keep H in such a position that the radius 

 H is in the direction of the wind. The sliders carry beneath 

 them wheels, B, C, whose planes are perpendicular to their 

 respective slits, and whose centres are beneath the pivots 

 joining the slits to the bar. [See figs. 1, 2, 3, Plate V. 

 Fig. 1 gives a perspective view of the instrument, omitting 

 some points; fig. 2 gives a view of the top of the instrument; 

 and fig. 3 gives a section of a slit and slider, and show- the 

 wheel carried by the slider.] The wheels B, C rest on a disk, 

 A (fig. 1), which revolves about a vertical axis immediately 

 below 0. The disk A is to be rotated by Bobinson's cups, or 

 some equivalent mechanism, so as to have a velocity propor- 

 tional to that of the wind. The pieces which carry the wheels 

 B, C should be allowed some play in a vertical direction; and 

 the contact of B and C with A can then be maintained either 

 by their own weight or by the use of a spring. The number 

 of rotations of B in a given time is proportional to the time- 

 integral of the resolved part of the wind in one direction (say, 

 north): and the number of rotations of C is proportional to 

 the time-integral of the resolved part of the wind in a direc- 

 tion at right angles to the first (say, west). 



Let O be the angular velocity of the disk A; a>, &/ the 

 angular velocities of the wheels B, C; m, m' the number of 

 their rotations in a given time t; L their radius, a the length 

 of the bar ; 6 the angle between the direction of the wind and 

 (say) the north; then bw = a^md . H, and £/&/ = « cos 6 . fi; 

 and the integrals required are 



r_Qsin0^= ('-oc ' 

 'o Jo a 



-TTill 



a 



* Communicated by the Physical Society, having been read at the 

 Meeting on June 10, 1882. 



