Page:Lake Ngami.djvu/311

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303
SHOOTING STAR—MIRAGE.

proceeded, I discovered a most magnificent shooting star, passing slowly in an oblique direction through space, with an immense tail attached to it, and emitting sparks of dazzling light. The fire by which I sat was exceedingly bright, and the moon clear and brilliant, yet they were both totally eclipsed by this immense body of light. Its great beauty and brilliancy might perhaps be best realized by saying that it was like a star of the second or third order when compared to the moon at full.

After a time, the pasturage being nearly exhausted in the neighborhood of the Hountop, we removed our camp a few miles southward to another periodical river called the Aamhoup. During our stay here we observed some very striking and singular horizontal refractions of the air. Once I saw an ostrich walking on the horizon line, while its double—clear and well defined—appeared immediately above it. Both the ostrich and its double, moreover, were divided into three different portions by as many dijfferent strata of air.

Again: regularly every morning, for nearly a month, the projecting ledge of a rock was converted into the semblance of a splendid and embattled castle. As the atmosphere became uniformly heated, the mirage melted away into a soft, watery haze.

In usual refractions the inverted image of an object generally appears above the object itself, but occasionally the effect is reversed. Captain Scoresby, the well-known Arctic navigator, once by these means discovered his father's vessel the day before it actually came in sight.

It has long puzzled the learned to account for the mirage. I believe, however, it is now pretty well known to arise from the unequal density and temperature of the lower strata of air.

The abundance of good water and pasturage had enabled our cattle to get into excellent condition; and as the season was now far advanced, and I was sufficiently well to travel,