226 SCIENTIFIC APPARATUS. 



Robinson's anemometer is practically the only velocity anemo- 

 meter now in use. The principle of the instrument is, that 

 the wind will cause a set of four hemispherical cups attached 

 to arms in the form of a cross to rotate with one-third of its own 

 velocity. 



It is evident that this instrument may easily be made self- 

 recording, as there is abundance of power available to move a 

 pencil. Beckley has added a windmill-vane arrangement to indi- 

 cate the direction, and the instrument so altered has been adopted 

 by the Meteorological Committee. Self-recording anemometers are 

 called Anemographs. 



Professor von Dettingen of Dorpat exhibits his new "Self- 

 recording Wind-Components Integrator." 



ATMOSPHERIC ELECTRICITY. 



This phenomenon is not observed at all stations. The nature of 

 the electricity present in the atmosphere can be determined by 

 a simple instrument such as the .Gold Leaf, Bennett's or Bohnen- 

 berger's electroscopes. In order to collect the electricity at a dis- 

 tance from the earth's surface, a metallic arrow with a conducting 

 string attached maybe shot into the air, the end of the string resting 

 on the plate of the electroscope ; Volta proposed to collect the 

 electricity by means of smoke; Sir W. Thomson, by means of 

 water dropping from a fine pipe. 



The principle of Thomson's two electrometers, viz., 



1. The Quadrant or Modified Divided-Ring Electrometer,. 



for observatory use. 



2. The Portable Electrometer- 

 will be found in the " Instructions in the Use of Meteorological 

 Instruments," p. 60. Thomson's electrometer may be described 

 as a combination of Coulomb's Torsion Balance and a Leyden Jar. 



Peltier's electrometer is described by Sir Charles Wheatstone,, 



