Integrating Anemometer. 485 



jection from the axle of the wheel W (fig. 3), which once in 

 every turn of the wheel pushes against the tongue Y and 

 brings it into contact with the tongue Z. On the table 

 (fig. 2) is another binding-screw p, which is not insulated. 

 Now suppose a truck H to be upon the North arm of the 

 cross. Its tongue Z is in electric connexion with the North 

 binding-screw cr, and the whole of that part of the system 

 is insulated from the table 0. Every time the w T heel W 

 turns round, contact is made between Y and Z; and the 

 effect is that the North a is put into electrical connexion 

 with the table 0, and therefore with the binding-screw p. The 

 general electrical system is shown in Plate XV., which gives a 

 front view of the box of counters, and a diagram of the anemo- 

 meter, batteries, and wires. The box contains four counters 

 lettered according to the cardinal points, and from the binding- 

 screws on one side (the right in the figure) insulated wires 

 pass to the corresponding insulated binding-screws cr on the 

 anemometer. From the binding-screws on the other side of 

 the box of counters insulated wires also proceed. The North 

 and South wires are connected with one pole of a battery, and 

 the East and West wires are connected with the same pole of 

 a similar battery. The other poles of the batteries are con- 

 nected by a wire which returns to the anemometer to the un- 

 insulated binding-screw p. If more convenient, the return 

 wire may of course be omitted, and the batteries and anemo- 

 meter be connected to earth. 



Let us now suppose the wind is blowing from about North- 

 east. The trucks H, K are now on the North and East arms 

 of the cross. The circuit through the South counter is complete 

 from the tongue Y through the table 0, the return wire, the 

 South counter, and then to the South binding-screw a and 

 South insulated rail R; but there it stops, and no current can 

 therefore pass through the South counter. The west circuit 

 is stopped in a similar manner. But in the case of the other 

 circuits, the insulated rail R is in contact with the wheel Q, 

 and so through P the circuit is carried on as far as the 

 tongue Z. Hence in the circuits through the North and East 

 counters a current passes whenever the corresponding tongues 

 Y and Z are pressed together, and the corresponding counter 

 marks one. 



To determine the value of the readings of the counters, we 

 may resort to measurements of the instrument or to direct 

 experiment. If we place one truck at its furthest distance 

 from the centre and rotate the spindle B a certain number 

 of times, and then note the increase in the reading of the 

 corresponding counter, there will be found a constant ratio k 



