Under this head I place some articles which could not be embodied
in this work; but which it may nevertheless be expedient to place
within the reach of certain readers. Among the articles referred to
is the theory of electricity, which I first published in 1848, and
which has been approved by the spirit of Franklin, and, in obedience
to his advice, inserted in this volume. Unfortunately, there are but
few persons sufficiently acquainted with the phenomena which form its
basis, and the technical language employed by professed electricians,
to find it agreeable to study the subject in question; but they may
qualify themselves to do so by studying the elementary works on this
branch of science.