It is possible, however, with the aid of our knowledge of static electricity, to arrive at hypotheses of a more than chimerical nature.  In the first place, that our sphere is a more or less electrified body is generally admitted.  More than this, it is demonstrated that the different parts of the earth’s surface and its enveloping atmosphere are variously charged.  As a consequence of these varying charges, there is a constant series of currents flowing through the various parts of the earth, which show themselves in such telegraph wires as may lie in the direction followed by the currents.  Such currents are known as earth currents, and present phenomena of a highly interesting nature.  But, apart from these electrical manifestations, there is generally a difference of electrical condition between the various parts of the earth’s surface and those portions of the atmosphere adjacent to or above them.  Inasmuch as air is one of the very best insulators, this difference of condition (or potential) in any particular region is in most cases incapable of being neutralized or equilibrated by an electric flow.  Consequently the air remains more or less continually charged.  With these points admitted as facts, the question arises, Whence this electricity?  There have been very many and various opinions expressed as to the cause of terrestrial electricity, but far the greater portion of such theories lack fundamental probability, and indicate causes which cannot be regarded as sufficiently extensive or operative to produce such tremendous effects as are occasionally witnessed.  I take it that we may safely regard the evolution of electricity as one of the ways in which force exhibits itself, that, in other words, when work is performed electricity may result.  When two bodies are rubbed together, electricity is produced, so also is it when two connected metals are immersed in water and one of them is dissolved, or when one of the junctions of two metals is raised to a higher temperature than the other junction.  I will go further than this, so far, in fact, as to maintain that there is a reasonable ground for supposing that every movement, whether it be of the mass or among the constituent particles, is attended by a change of electrical distribution; and if this is true, it may easily be conceived that inasmuch as motion is the rule of the universe, there must be a constant series of electrical changes.  Now, these changes do not all operate in one direction, nor are they all of similar character, whence it is that not only are there earth currents of feeble electro-motive force, but that this E.M.F. is constantly varying, and that, furthermore, electricity of high E.M.F. is to be met with in various parts of the atmosphere.