16 
POPULAR SCIENCE REVIEW. 
meteoric display ; for a true cometary shower can only endure a 
few nights. The agreements, therefore, are conjectured to result 
from pure accident, for obviously there must arise many similar 
positions amongst the large number of radiant points at present 
comparable. This is rendered still more probable by the fact, 
that even in some cases where the accordance is good, both in 
position and epoch of the radiant centre, the comet’s paths were 
very distant from the Earth, never approaching it within many 
millions of miles, so that it is difficult to understand how the 
particles are encountered at such remote distances from the 
nucleus. A shower of meteors from Corona in April was found 
to coincide with the radiant point of the Great Comet of 1847 ; 
but the accordance is otherwise defective and vitiated by the 
fact that the comet’s nucleus ‘ in its node and perihelion almost 
grazed the body of the Sun : and only the lengthy tail which it 
swept or wheeled round with it can be supposed to have reached 
the orbit of the Earth.’ * Numerous other instances might be 
cited in which the orbits of comets falling far within the Earth’s 
path cannot possibly occasion a meteor- shower, unless, as Weiss 
and Schiaparelli have considered likely, 4 some portions of the 
cometary substance, repelled from their proper orbits by the 
Sun in the form of the tail and other luminous appendages 
emitted by the comets near their perihelion passages, may have 
extended to such a distance in their orbit planes as to intersect 
the orbit of the Earth.’ f We are ignorant at present of all the 
conditions under which meteor- showers are produced, and of 
the many varieties existing among them ; but it appears pro- 
bable that the meteoric particles may be sometimes distributed 
over a considerable width of orbit by the trains and other 
luminous projections from comets during their circumsolar 
passages. 
The apparent long duration of meteor radiant points has 
struck nearly every observer who has entered fully into this 
department. Mr. Greg has pointed out, that according to his 
own experience, the average duration is far beyond the limits 
considered probable. $ He states that in his own catalogue of 
meteor -showers deduced from 2000 shooting -stars seen in 
England during the years 1849-67 the average duration for 
forty radiant points (occurring at all periods of the year) is 
thirty-three days ; and there are twelve showers reaching fifty- 
four days, some of which, however, he regards as not really one 
shower. He found that in not a few cases the period would 
seem to extend for two or three months without any special 
intermission. Dr. Schmidt’s results confirm Mr. Greg’s, for of 
the forty-five showers included in his catalogue the mean 
* B. A. Report on Luminous Meteors , 1877, p. 165. f Id* 1873, p. 402. 
X Monthly Notices R.A.S . , vol. xxxviii., p. 351. 
