"At Lord Wrottesley's observatory, in Staffordshire, about 530 feet above the sea, there appears to be considerably less strength of wind at any given time, when a gale is blowing _generally_, than occurs simultaneously at places along the sea-coast: whence the inference is, that undulations of the land's surface and hills, diminish the strength of wind materially by frictional resistance. "All the synoptic charts hitherto advanced at the Board of Trade exhibit a marked diminution of force inland compared with that on the sea-coast. Indeed, the coast itself offers similar evidence, in its stunted, sloping trees, and comparative barrenness."[14] CHAPTER XIV. INSTRUMENTS FOR INVESTIGATING ATMOSPHERIC ELECTRICITY. =131. Atmospheric Electroscope.=--The simplest instrument for ascertaining at any time the electric condition of the atmosphere is an electroscope composed of two equal pieces of gold leaf, suspended from a brass support, and insulated, as well as protected from the movement of the air, by a glass covering. Fig. 90 represents such an instrument. The cap of the brass support is fitted for the reception, in the vertical direction, of a metallic rod, not less than two or three feet in length. The top of the rod carries a clip. The instrument acts according to the law, that bodies similarly electrified repel each other; but when dissimilarly electrified, they attract each other. To make an observation, the instrument is placed in the open air, and a lighted piece of cigar fusee, or touch-paper, is fixed in the clip. The electricity of the air is collected by the substance undergoing combustion, and conducted by the rod to the gold leaf; and the pieces, being similarly electrified, separate more or less according to the amount of electricity present. The kind is determined by the effect of either an excited stick of sealing-wax or rod of glass upon the electrified gold leaf. A rod of glass, when rubbed briskly with a silk handkerchief or piece of woollen cloth, becomes positively electrified, or excited, as it is termed. A stick of sealing-wax, similarly treated, acquires the negative state. If, therefore, an excited glass rod be presented to the cap of the instrument, and it cause the pieces of gold leaf to diverge still further, the electric state of the air must be analogous to that of the glass, that is, _positive_; if they approach, it is _negative_. On the contrary, if a stick of sealing-wax be used, the pieces will be repelled more apart if they have acquired negative electricity from the air; and they will converge if they have a positive charge. [Illustration: Fig. 90.] By means of this very simple instrument, meteorological observers can readily ascertain the electric condition of the lower air at any time. NOTE.--A book containing strips of gold leaf is sent with the Electrometer to replace the gold leaves when torn or broken in use.