1897.] on the ApproacMug Beturn of the November Meteors. 339 



When the Meteors will return. 



The immense procession takes two years to pass the point where 

 it pours across the earth's orbit. This point the earth reaches every 

 year about the middls of November, and accordingly, when the 

 meteors return the earth will certainly, in two successive years, pass 

 through the stream, and may also encounter the front or rear of the 

 procession in a third year. In this way we may count on having 

 great meteoric displays on whatever is the advancing side of our 

 earth in each of two successive years, in November 1899, and in 

 November 1900, with perhaps a third display in either 1898 or 1901. 

 In the middle of November of the year 1898 the moon will be absent, 

 and if by good fortune the head of the meteoric stream shall have 

 arrived so soon, which, however, is doubtful, we may expect an immense 

 display then on one half of the earth. In 1899, when it appears 

 certain that the stream will be encountered, there will unfortunately 

 be moonlight, which will detract from the splendour of the display, 

 though it need not take away our prospect of securing invaluable 

 photographic records in that year, since it has been found that such 

 photographs may be taken even in strong moonlight. 



Sporadic Leonids. 



Another matter to which attention was invited was that of the few 

 scattered Leonids which the earth meets with every year, and not 

 only in the years of the great displays. Their presence may be 

 accounted for as follows. 



The meteoric stream is about 100,000 miles across — more than a 

 third of the way from the earth to the moon — and through it the 

 earth passes obliquely, occupying about five hours in the transit. 

 The earth intercepts some of the meteors, which plunging with 

 immense speed into our atmosphere, are first heated by the friction to 

 brilliant incandescence, and then dissipated in vapour before they 

 can get within miles of the earth's solid surface. This produces 

 the splendid spectacle which we are privileged to witness on such 

 occasions. But many as are the meteors which the earth intercepts, 

 those are immensely more numerous which pass close enough beside 

 it to be bent by its attraction a little out of their previous orbit — 

 only a little, however, on account of the enormous speed with which 

 they shoot past the earth, a speed of about 45 miles a second — so that 

 each is not so much as three minutes in darting past the earth. 

 The earth has plunged some sixty or seventy times through the 

 stream, and has thus diverted from their natural course a vast number 

 of the meteors. But however great this number may be, the number 

 of those which were too far off to feel any influence from the earth is 

 immeasurably greater. In fact, the meteoric stream is about as long 

 as from Jupiter to the earth, so that the earth when it passes through 

 the stream can affect but a very short piece of its whole length. 



Those Leonids that have been thus affected are they that have 



