As soon as one wave passes,
another, of the reverse polarity, always succeeds. I have never known
this to fail, and it may be set down as an invariable rule. When the
poles of the aurora are in unison with the poles of the current upon
the line, its effect is to increase the current; but when they are
opposed, the current from the battery is neutralized,--null. These
effects were observed at times during Saturday, Saturday evening, and
Sunday, but were very marked during Sunday evening.
It is hardly necessary to add here, that the effect of the aurora
borealis, or magnetic storm, is totally unlike that of common or free
electricity, with which the atmosphere is charged during a
thunderstorm. The electricity evolved during a thunder-storm, as soon
as it reaches a conductor, explodes with a spark, and becomes at once
dissipated. The other, on the contrary, is of very low tension, remains
upon the wires sometimes half a minute, produces magnetism, decomposes
chemicals, deflects the needle, and is capable of being used for
telegraphic purposes, although, of course, imperfectly.
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