In his recent lectures on Solar Physics, Professor Stokes, while expounding his theory of the connection of magnetic disturbances, auroræ, and earth currents, says:—“We might not have tension enough to produce such a discharge (that is, a flash of lightning), the resistance to the passage of electricity from one portion of the air to another, which at any rate would be comparatively dry compared with what we have in warm latitudes, would prevent it by itself alone.” Professor Stokes subsequently remarked in a letter to Nature: —“These words, without actually asserting, seem to imply that the resistance to such a discharge through moist air would be less than through dry. My attention has been called by a friend to the fact that it has been found by experiment that moist air insulates as well as dry. I have not met with experiments tending to show whether the resistance to a disruptive discharge is the same or not in the two. Be that as it may, it does not affect what follows; for we know, as a fact, that thunderstorms are absent in high latitudes.”