New York Weather Bureau. 370 



Actinometer. — An actinometer or sunshine recorder (Richard's) 

 is mounted on a shelf out of a south window of the col- 

 lege. The intensity of solar heat is measured by the differ- 

 ence in temperature between two glass bulbs 4 inches in 

 diameter, placed side by side, one of which is coated with 

 lamji-black while the other is silvered. The two have the 

 same temperature (nearly) when the sky is overcast, but 

 the black bulb absoirbs the heat of solar rays more rapidly 

 than the bright under a clear sky. Each bulb contains a 

 coil of copper tube filled with alcohol, and communicating with 

 separate tubes similar to those of the thermographs, each of which 

 has its reoopdiing lever and pen, whose tracings are made on a 

 cylinder rotating ooce 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 pro- 

 vided eighteen years ago by the directoir, 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 carriage moves vertically 

 down the length of the cylinder in 24 hours; and since the cylin- 

 der turns with the vane, the pencil tracing upon a sheet of 

 paper which is wrapped around the cylinder, furnishes a continu- 

 ous 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 



