March 4, i 



NA TURE 



419 



shooting-stars have belonged to astronomy. The November 

 meteors were admitted a new constituent of the solar 

 system. Three years later, M. Ouetelet, of Brussels, 

 found that shooting-stars are to be seen in unusual 

 numbers about -August lo of each year. A few months 

 afterwards Mr. Herrick made independently the same 

 discox'ery ; but he also told us of star-showers in April 

 and January. What Brandes had seen in December 

 179S led Mr. Herrick. moreover, to e.\pect a like shower 

 in other Decembers, and he asked that shooting-stars be 

 looked for on December 6 and 7, 1838. This shrewd 

 guess was justified, for on the evenings of those days 

 hundreds of these meteors were seen in .America, in 

 Europe, and in Asia by persons thus induced to look for 

 them. These shooting-stars also had once been parts of 

 Biela's comet, though this fact was not dreamed of at 

 that time. 



In the course of time we came to know more about the 

 meteoroids ; that in general they moved in long orbits 

 like comets, rather than round one^ like planets ; that 

 some of them were grouped in long, thin streams, many 

 hundreds of millions of miles long, and that it was by the 

 earth's plunging through these that we have star-showers ; 

 that the space travelled over by the earth has in it every- 

 where some of these small bodies, probably the outlying 

 members of hundreds of meteoroid streams. 



Also the periodic time and the path of the stream of 

 November meteoroids were found out. Then came the 

 interesting discovery that in this stream, and in that of 

 the August meteoroids, lay the paths of two comets. 

 Then Dr. Weiss of Vienna showed that the meteors seen 



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by Brandes in 1798, and by Herrick in 183S, as well as 

 many meteors seen near December i of other years, and 

 the Biela comets, all belonged to each other. 



It is then properly a part of my story to show you the 

 behaviour of one of the streams of meteoroids. Stand- 

 ing several hundreds of miles away, see them enter the 

 upper atmosphere. They are entirely unseen until they 

 strike the air. They then come down like drops of fiery 

 rain a few miles, in parallel lines, burning up long before 

 they reach the ground (see Fig. 9). The air is in fact a 

 shield, protecting the men below from a furious bombard- 

 ment. The region of the luminous tracks is many miles 

 above that of the highest mountains. 



Go farther away. Parallel lines may show the paths of the 

 meteoroids (Fig. 10), though the bodies themselves are too 

 small to be seen. They strike a little way into the air, to 

 some persons coming from the zenith, to some coming 

 obliquely, to some skimming through the upper air — and 

 unseen by all upon one whole hemisphere. 1 need hardly 

 remind you that sunlight, and twilight, and clouds often 

 come in to prevent the seeing of the star-flights by 

 persons below. 



Go still farther away. From outside look in toward 

 the sun upon the earth and meteoroid stream. The 

 meteoroids in fact are not to be seen. The stream is of 

 unknown depth, perhaps millions of miles deep. Its 

 density increases in general toward the centre. We cross 

 the densest part of the November stream in 2 or 3 hours, 

 and the whole of it in 10 or 15 hours, while the passage 

 of the August stream requires 3 or 4 days. The Biela 

 stream is crossed obliquely, the meteoroids overtaking 



the earth. The August stream is nearly perpendicular, 

 and the November stream meets the earth. 



Again go still farther away, out to the point from which 

 we first looked down upon the earth and comet. We then 

 see (by the mind's eye) the meteoroids strewn along the 

 elliptic orbit of the comet for hundreds of millions of 

 miles, forming a stream of unknown breadth, but in the 



scale of the first figure shown you about ^ of an inch in 

 thickness. 



Come back now and stand inside the stream, at its 

 densest part. You in fact see nothing ; but the ineteoroids 

 are all about you scattered quite evenly, and distant each 

 from its nearest neighbours 20 or 30 miles. They all 

 travel the same wav and with a common motion. 



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Once more change your place and look up from the 

 earth's surface. The meteoroids can now be seen, for 

 when they strike the air they burn with intense light, 

 becoming'shooting-stars. As it is from this position only 

 that we ever see them, note their behaviour with more 

 care. A shooting star coming toward you appears only as 

 a bright stationary point in the sky. That point is a 



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marked one in every star-shower, and is called the radiant. 

 The meteors to the right and left of the stationary one 

 are, in fact, moving in the common direction, but they 

 seem to move in the sky away from the radiant (Fig. 11). 

 In other words, the tracks produced backward will all 

 meet in one point in the sky (Fig. 12). This radiant-point 

 may be in the horizon, or in the zenith, or at any place 



