Integrating Anemometer. 483 



to pass over the slits S, and yet always to keep the pivot E 

 well within the base formed by the remaining four wheels, so 

 that it may be perfectly steady. On the underside of the 

 table are similar tram-lines, N; and trucks (K) run in these 

 tram-lines, each on five wheels, V. Fig. 3 shbws one of these 

 trucks seen from below, with portions of the tram-lines N. 



Fig. 4 is an elevation showing an end view of the trucks 

 H and K, with a portion of a section of the table across a 

 slit S. Two rods, T, of which the ends are shown in fig. 3, 

 and of one of which a side view is shown in fig. 4, are rigidly 

 connected with H and pass through the slit S and through 

 holes in K. Spiral springs surrounding the rods T and rest- 

 ing on the heads of the rods press K upwards, and make it 

 keep its position exactly and firmly under H. Each truck, K, 

 carries firmly fastened to it two pieces of brass, L (see figs. 1, 

 3, 4); and between these pieces is pivoted a bar with arms J, 

 and between these arms is pivoted a wheel W, which is carried 

 in a vertical position also at right angles to the slit through 

 which T passes. A rod I connected with K is surrounded by 

 a spiral spring which presses on J, and so keeps a steady 

 pressure between the wheel W and the disk X. The pivots 

 of J and W are so placed that, when W touches X, these 

 pivots all lie in one horizontal plane, and the point of contact 

 of W with X is vertically below the centre of the pivot E 

 (figs. 1,2). 



Now suppose the wind to lie between North and East, and 

 the direction from which it blows to make an angle with 

 North. Let 12 be the velocity of the wind. Then the resolved 

 parts of the wind towards North and East will be 12 cos and 

 12 sin respectively. But if 8 be the length of the bar F 

 (fig. 2) measured between the centres of its pivots E, it is 

 easily seen, from the diagram in the margin, that the distances 

 of the wheels W from the centre 

 of the disk X (fig. 1) are 8 cos 

 and 8 sin towards the North and 

 East respectively. Now the 

 speeds of the wheels W are pro- 

 portional to the speed of the disk 

 X on which they roll multiplied 

 by these distances, and the speed 

 of the disk X is proportional to 

 the velocity 12 of the wind. 

 Hence the speeds of the wheels 

 W are proportional to 8 cos 0.12 

 and 8 sin 0.12 respectively ; that 

 is, they are proportional to II cos and II sin 0, which are the 

 resolved parts of the velocity of the wind. 



