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Page:Popular Science Monthly Volume 18.djvu/194

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THE POPULAR SCIENCE MONTHLY.

source of compensation for the expenditure of its materials upon the earth. But, though many millions of the atoms are annually consumed in our atmosphere, the effect of the thinning out will be very gradual in making itself appreciable, for, as compared with the vast assemblage which constitutes the main ring, the proportion which encounters the earth is small indeed. As it is enveloped in the stream, comparatively few of the meteors are actually intercepted. By far the greater number pass by untouched. If a ball is thrown up in a thick shower of rain, it will only encounter a few drops. This may be taken as an illustration. The earth, with its diameter of 8,000 miles, can only meet with a few meteors in its rapid flight through a zone exceeding 10,000,000 miles in width.

The period of the August meteors is uncertain. Their distribution appears to have been so effectual that the element can not be determined. Some years give plentiful showers, but there have been no decided traces of regularly recurring maxima, as in the case of the Leonids. This may possibly be explained by the fact that the period is a long one, and would not become defined until after centuries of research. Comet III, 1862, which shows an exact resemblance of orbit to this system, was computed by Oppolzer to have a period of 121ยท5 years; and, as there occurred a fine display of the August meteors in 1863, we can not anticipate its periodical return until about 1964, if the calculations are reliable.

The August Perseids have been more frequently observed than any other system of shooting-stars, from the fact that they are visible every year with more or less distinctness, and that, as an annual shower, they can not be surpassed by any other display. The two celebrated streams of November 13th and 27th, occasionally giving rise to showers of great splendor, are periodical in character, though it is extremely probable that a few of their meteors encounter the earth at the regular return of the dates; notwithstanding that they may elude observation in consequence either of moonlight or cloudy weather, which, indeed, generally offers some impediment to success. But the August meteors recur annually with considerable intensity, and had attracted attention at a very remote epoch, though the phenomenon was not systematically studied until later times. It was reserved for Heis at Aix-la-Chapelle to more thoroughly investigate the meteors of August, for the previous observers, though they had ascertained the fact that the month was notable in this respect, had yet neglected to obtain any important data with regard to the number or directions of the meteors seen. Schmidt also, at Bonn, began assiduously to devote himself to this special line of inquiry. The particular night in August when the meteors were most plentifully distributed was found to be the 10th, though the numbers were subject to considerable variations in different years. Schmidt, from an average of several years of observations, gave the following as the horary number of falling stars