I will try to make myself clear upon this point. It makes no
difference, in working the Morse, or any other system of _magnetic_
telegraph, whether we have the positive or the negative pole to the
line; but, whichever way we point, the same direction must be continued
with all additional batteries we put upon the line. Now if we put a
battery upon the line at Boston, of, say, twenty-five cells, and point
the positive pole eastward, and the same number of cells at Portland,
pointing the positive pole westward, the current will be null, that is
to say, each will neutralize the other. Now the aurora, in presenting
its positive pole, we will say, increases the current upon the line
beyond the power of the magnet-keeper-spring to control it, and thus
prevents the line from working, by surfeiting it with the electric
current; until, presently, the wave recedes and is followed by a
negative current which neutralizes the battery current, and prevents
the line from working for want of power. It is plain, therefore, that,
if the batteries be taken off, the positive current of the aurora
cannot increase nor the negative decrease the working state of the line
to the same extent as when the batteries are connected; but that,
whichever pole is presented, the magnetism can be made use of by the
operator for the ordinary duties of the line.
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