We had been steering our new course about an hour when it became apparent that a change of weather was brewing, though what the nature of the impending change might be it was, for the moment, somewhat difficult to guess.  The appearance of the sky seemed to portend a thunderstorm, for it had rapidly become overcast with dense masses of heavy, lowering cloud, which appeared to have quite suddenly gathered from nowhere in particular, obscuring the stars, yet not wholly shutting out their light, for the forms of the cloud-masses could be made out with a very fair degree of distinctness, and it would probably also have been possible to distinguish a ship at the distance of a mile.  It was the presence of this light in the atmosphere, emanating apparently from the clouds themselves, that caused me rather to doubt the correctness of the opinion, pretty freely expressed by the men, that what was brewing was nothing more serious than an ordinary thunderstorm, for I had witnessed something of the same kind before, on the coast, but in a much more marked degree, it is true; and in that case the appearance had been followed by a tornado, brief in duration, but of great violence while it lasted.  I therefore felt distinctly anxious, the more so as it was evident that the wind was dropping, and this I regarded as a somewhat unfavourable sign.  I hailed Simpson, and asked him what he thought of the weather.