430 TERRESTRIAL PHYSICS. 



raius in summer on these plains. Showers would come up as tliey do 

 in the eastern part of the United States, but seemed to be drawn and 

 swept along the sides of the mountains, where they expended their 

 moisture, giving only to us in the prairies the comfort of tlieir shadows. 

 I noticed this in a residence of some five'years in the Walla-Walla Val- 

 ley, on the southern boundary of the great plain of the Columbia, as 

 well as in the many valleys of Montana. Living, as I have for several 

 summers, under canvas, and my business calling my attention to the 

 clouds and the trees, my experience there corroborates my observation 

 in W^alla-Walla, as showing that the showers of summer are of much 

 more frequent occurrence along the mountain-sides, and are always of 

 longer duration among the timbered peaks and foot-hills than in the 

 lower and treeless portions of the country. The trees grow always along 

 the streams, where there is a constant supi)ly of water, although the soil 

 may not dilfer in any material respect from that in the immediate \'i- 

 cinity, which, being dry and unnourished by rains, afford no nutriment 

 to the seeds of the cottonwood, the pine, or the fir. Not only the ab- 

 sence of rains in summer, but the absence of snows in winter, are a pre- 

 ventive to the growth of forests. Thus, we see these valleys are sel- 

 dom visited by snows of any depth, from twelve to tweut3-four inches 

 being the limits of deposit in ordinarj^ winters, and frequently the fall 

 over their surfaces does not reach a depth of over five or six inches, 

 while in the elevated lands of the mountains in the timber, snows of from 

 three to seven feet are of almost universal occurrence every winter, and 

 in the northern latitudes referred to, while the altitude is not so great, 

 still the snow deposit is as great and as widely diffused. 



As another evidence of moisture being a controlling element in the 

 growth of trees, wherever a sjiring starts out of a mountain-side, other- 

 wise treeless, a clump of timber marks the spot, and is an almost sure 

 sign of its presence; and wherever a tree is i)lanted and supplied with 

 its requisite amount of water, the growth is as thrifty, as healthy, and 

 as enduring as in its native forest. 



INFLUENCE OF THE AIROKA ON THE TELEGRAPH. 



By W. D. Sargkxt. 



Haeeiseukg, Pennsylvania, Septemlter 27, 1870. 



I take the liberty of laying before you some crude observations of 

 mine on the effect of the aurora on telegraph lines on the nights of the 

 24th and 25th instant. 



Saturday, September 24th, the wires were very much interrupted all 

 the evening, and we supposed a storm was gathering in the west, but 

 the appearance of the aurora between 8 and 9 p. m. discovered the real 

 cause of the trouble. The light and flashes increased in brilliancy and 



