186 ANNUAL REPORTS OF DEPARTMENT OF AORTCULTURE. 



improved from time to time, aKhough the general type and design 

 have remained the same. 



Besides the improvement in the instrumental equipment at the 

 regular Weather Bureau stations a good type of thermometer shelter 

 is fast being furnished to the cooperative climatological stations, 

 which now number 4,000, and of which 3,100 are equipped with the 

 standard shelter, in addition to the thermometers and rain gauges 

 used at those points. 



Beginning in 1900 the equipment of storm-warning display sta- 

 tions has been steadily improved by the installation of steel towers 

 and the use of high-power oil and electric lights for display of flags 

 and night signals. More than 200 of these towers are in use at the 

 present time. 



With the beginning of aerial studies in the winter of 1895, a stand- 

 ard type of construction of the Hargrave box kite was perfected and 

 has been employed without appreciable modification in the subse- 

 quent work of the bureau, as well as at a number of European 

 observatories. The same is true in regard to a light form of meteoro- 

 graph that is sent up with the kites for recording the pressure, tem- 

 perature, humidity, and wind velocity. In the course of the aerial 

 work several excellent forms of windlass were designed for winding 

 and unwinding the steel piano wire used in the kite ascensions. 



Earthquake vibrations have been recorded in a more or less com- 

 plete manner at the Washington office of the Weather Bureau for 

 many years. In 1903 a modern type of seismograph of superior 

 design was installed. The equipment was subsequently improved by 

 the installation of a more sensitive new type of seismograph designed 

 and constructed in the Instrument Division, and records have been 

 obtained of all the important earthquakes that have since occurred. 



Several useful improvements in methods and devices for observing 

 and measuring evaporation were also developed and used in connec- 

 tion with the special evaporation studies conducted by the Weather 

 Bureau in 1907-1909. 



Observations of the intensity of solar radiation began with the 

 use of the Angstrom pyrheliometer. An improved type of disk 

 pyrheliometer has been developed in the Instrument Division, and 

 this form of instrument is now being used at Mount Weather, Va. ; 

 Madison, AVis. ; Lincoln, Nebr. ; and Santa Fe, N. Mex. 



The accuracy of anemometer records at very high wind velocities 

 has never been completely established. This work has recently been 

 undertaken with the aid of a large whirling machine set up at Mount 

 Weather, Va. Through its use a test will be made of all the impor- 

 tant types of anemometers at velocities up to and beyond 100 miles 

 per hour. 



A special structure of ornamental character was devised in 1908 

 for the purpose of displaying meteorological instruments and weather 



