New York Weather Bureau. 419 



bulb contains a coil of copper tube filled with alcohol, and com- 

 municating with separate tubes similar to those of the thermo- 

 graphs, each of which has its recording lever and pen, whose 

 tracings are made on a cylinder rotating once in two days. The 

 differences between the temperatures traced by the two levers 

 indicate the intensity of the solar radiation. 



Wind Registers. — Two sets of wind registers are in use at 

 the central station, each set furnishing an automatic record both 

 of velocity and direction. Firstly, the instruments provided 

 eighteen years ago by the director, and whose records have since 

 been maintained, are mounted about 8 feet above the ridge of the 

 engineering building and 75 feet above the ground. The wind 

 vane has for its axis a rod which is brought down through the 

 roof, and carries at its lower extremity a cylinder about 3 inches 

 in diameter and 9 inches long. A pencil held in a suitable car- 

 riage moves vertically down the length of the cylinder in 24 

 hours; and since the cylinder turns with the vane, the pencil 

 tracing upon a sheet of paper which is wrapped around the cylin- 

 der, furnishes a continuous record of the wind direction. 



The anemometer, which is of the Robinson pattern, has four 

 hemispherical cups carried on spokes radiating from a vertical 

 axis. Rotation is caused by the greater force which the wind 

 exerts upon the concave over that upon the convex sides of the 

 cups; and when the number of revolutions indicates 1 mile of 

 wind travel, an electric contact is made by a mechanism 

 attached to the axle of the anemometer. Wires attached 

 to the instrument transmit the current to a Gibbon reg- 

 ister located on the first floor of the building. A screw- 

 thread is cut upon the axis of the recording cylinder 

 of this register, and as it is rotated by clockwork at the rate of 

 one turn in 6 hours, the screw also gives it a motion lengthwise 

 with the axis, so tbat a pen in a fixed position would trace a spiral 

 line around its surface. In fact, the recording pen is attached to 

 the pole piece of an electro-magnet in circuit with the anemometer, 

 and hence, at every mile-contact, a notch is made in the spiral line 



