i82 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 con- 

 sumed 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 en- 

 counters 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 121*5 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 ob- 

 servations, gave the following as the horary number of falling stars 



