360 



THE POPULAR EDUCATOR. 



America ; the news of them, however, soon spread, and directed 

 the attention of astronomers in all countries to the subject. The 

 fact of these grand displays having occurred for three consecu- 

 tive years, about the 13th of November, naturally attracted notice, 

 as it seemed to indicate a periodical character. Accordingly, on 

 that date in the following year a strict watch was kept by many 

 astronomers, and though no very marked display occurred, the 

 numbers seen were found to be very far above the average. 

 Continued observations have 

 shown that at this period there 

 is always a much larger dis- 

 play of these bodies than at 

 other times of the year. By 

 examining likewise the records 

 of these showers it was noticed 

 that the grand displays seemed 

 to take place about every 

 thirty-three years, sometimes 

 being seen for two or three 

 consecutive years. It was 

 accordingly suggested that not 

 improbably a brilliant display 

 might be seen in 1866, and 

 though the numbers seen were 



not nearly so great as in 1833, 



the display was very grand and 



beautiful, so that all who had watched through the night felt 



amply repaid for their trouble. 



Nearly all appeared, as in previous instances, to radiate from 

 the star 7 in Leo, and close to this spot many faint ones were 

 observed, some seeming just to appear and vanish again, without 

 having changed their position perceptibly. These were evidently 

 travelling directly towards the Earth, and hence their trains 

 were so foreshortened as to be invisible. 



We eee, then, the main facts in connection with the appear- 

 ance of these meteors, and the problem now is to find what we 

 are to learn from them as to the nature and movements of these 

 bodies. As we have seen, several facts seem most clearly to 

 show that their origin is beyond the surface of the Earth ; and 

 the annual periodicity further indicates that in certain parts 

 of its orbit the Earth is passing througli a portion cf space 

 which is specially crowded with them. 



By noting the position of tho spot whence they appear to 

 radiate, we learn tho direction in which they are coming, and 

 we find that tho Earth seems actually to bo in the midst cf a 

 stream of them. The opinion now received is that there is a 

 ring of these bodies revolving around tho Sun. This ring is 

 about the size of the orbit of the Earth ; it is inclined to tho 

 plane of tho ecliptic at an angle of about 17, cutting it just in 

 the part in which the Earth is situated on the 13th of November, 

 PO that at this period the Earth is actually passing through tho 

 ring, as represented in Fig. 32. The dotted lines wo will 

 suppose to represent the zone 

 of meteorites, distributed un- 

 evenly, but still for the most 

 part kept within narrow limits. 

 These are moving along from 

 left to right. About the 13th 

 of November the Earth is 

 moving along the part A B of 

 its orbit, in the direction shown 

 by the small arrows. It there- 

 fore meets the stream of 

 meteors, which will, of course, 

 all appear to radiate from one 



point. Their uneven distribution in the stream will account 

 for the constant fluctuations in number, and at any period 

 they will only be visible to that part of the Earth which 

 is directed towards them. This explanation is not sufficient 

 to account for the fact of a star-shower being so much 

 more brilliant one year than another, nor for the periodical in- 

 terval of thirty-three years. If, however, we suppose that in 

 one part of the ring they are clustered together more thickly 

 than in the rest of it that there is, in fact, in one part a rich 

 group of these bodies, and that this group revolves in its orbit 

 in about eleven days less than the Earth takes the whole will 

 be explained. This group extends over some small portion of the 

 ring, so that at times the Earth may for two or three successive 



years pass through or near the dense portion. It gains, how. 

 ever, about 12 annually, so that for some thirty years the 

 Earth only passes through the portion where they are less 

 thickly crowded. 



Besides the 13th of November, there are other periods at which 

 large numbers of these bodies may be seen. The 9th llth of 

 August is such a period, and though the numbers then seen are 

 usually less than in November, the display is more certain and 



more uniform. There appear 

 to be several of these rings of 

 meteorites through which the 

 Earth passes at different pe- 

 riods, and a considerable num- 

 ber of radiant centres from 

 which they diverge have been 

 noted. Some astronomers sup- 

 pose that the August and No- 

 vember meteors are parts of the 

 same ring, which therefore cuts 

 the Earth's orbit in two points. 

 The opinion that they are two 

 separate rings is, however, more 

 generally received. 



We have now to inquire as 



rig. 32. fo the nature or constitution 



of these bodies, and concern- 

 ing this not much can be said. It is believed that they 

 are small, solid bodies, revolving round the Sun as already 

 stated. As they are travelling in a contrary direction to the 

 Earth, the velocity with which they enter our atmosphere 

 is very great. The resistance of the air soon checks this 

 motion, but by the friction thus produced the body is so in- 

 tensely heated, that it becomes luminous, and ultimately is 

 entirely consumed. The average height at which they become 

 visible is about seventy miles, and their course is about thirty 

 miles. The weight of most of them is believed to be very 

 small, possibly not more than a few grains. There are, how- 

 ever, a few which are much larger, and, owing to their size, 

 pass unconsumed through the atmosphere, and fall upon the 

 Earth's surface. These are usually distinguished as meteo- 

 rites, and are sometimes divided into aerolites, or meteoric 

 stones, and aerosiderites, or pieces of meteoric iron. 



It is not known whether these bodies, like those already 

 described, move in elliptic orbits, though it has been observed 

 that they too are somewhat periodical. 



The fall of many of them has been recorded, and the masses 

 themselves are in many instances carefully preserved. When 

 the body has been seen to fall, a loud report has frequently 

 been heard accompanying it, and sometimes fragments have 

 been scattered over a large area, showing that while falling 

 the meteorite has exploded. In April, 1803, a brilliant fire- 

 ball was seen in Normandy, travelling very rapidly, shortly after 



which a loud explosion was 

 heard, and a great number of 

 pieces of stone fell to the 

 ground, nearly 3,000 being col- 

 lected. 



When picked up soon after 

 tlieir fall, these bodies are 

 usually found to be intensely 

 hot. On chemical examination 

 no new elements have been 

 discovered in them. The ma- 

 jority are found to contain 

 iron, usually in a very large 



proportion, and nickel is nearly always foand associate! 

 with it. 



ECLIPSES. 



We have thus completed our survey of the solar system, and 

 of the different bodies which compose it. Our attention must 

 now be directed to the phenomena of eclipses, which have already 

 been referred to when treating of the Moon. 



The Earth and Moon are, as we have seen, constantly chang- 

 ing their positions, both with respect to the Sun and to one 

 another, and hence at times it happens that all three are in 

 the same straight line. If in this case the Sun is at one ex- 

 tremity of the line, the body at the other extremity will for a 

 time be deprived of its light, being in the shadow of the central 



Fig. 33. 



