had changed to a purplish-blue, and as night approached came the usual lightning-flashes; my impression was we were going to have a storm, but there were no signs of clouds all night, and a clear sky the next day. On the following day we treked fifteen miles more to the north, and in the afternoon observed, just above the horizon, a line of clouds, similar to those I had seen the day before in the same position, and as evening advanced they appeared to have dispersed, as they became blended with the evening tints, and a casual observer would declare, with every appearance of truth, that there were no clouds to be seen in the sky, although he would see the lightning-flash only, as in no case when these apparently cloudless flashes come, is spark or electric fluid visible. I have been exploring constantly the whole of South Central Africa for twenty-five years, out in the open air nightly; not an evening escaped my observations, therefore I write with some degree of confidence when I state no electric spark is ever seen with this lightning, in consequence of the distance, and partly below the horizon, and occasionally, but very seldom, in the stillness and quiet that pervades everything, the air perfectly calm, the distant nimble of thunder may be heard, and the clouds before morning have vanished. I followed these observations for months, and whenever any clouds were seen just above the horizon before the sun went down, they appeared to vanish as the evening tints deepened. The same result followed year after year.