138 Meteoric Astronomy. [April, 
We may begin, then, by considering the first important 
fact tending to prove the extra-terrestrial nature of meteors 
and shooting-stars,—the circumstance, namely, that meteoric 
displays occur commonly on certain days of the year. 
It had been noticed in very early times that a display 
of shooting-stars nearly always occurs on the night of 
August 10. This being known in calendars as St. Law- 
rence’s Day, the meteors which fall on that day have been 
called the tears of St. Lawrence. Among astronomers, 
however, they are more commonly called the Perseides, for a 
reason presently to be cited. Not so early, but still many 
years before the true theory of meteors began to be recog- 
nised, it was known that on or about the 12th and 13th of 
November, shooting-stars are commonly seen. When Hum- 
boldt, after witnessing the remarkable display of 1799, 
invited specia] attention to this circumstance, ancient 
records were examined, and it was found for several centuries 
this particular part of the year had been characterised by 
star-showers. ‘‘ Time out of mind,” says Sir John Herschel, 
“‘those identical nights more often, but sometimes those 
immediately adjacent, have been habitually signalised by 
such exhibitions.” 
It cannot be too often insisted upon,—since doubts are 
frequently expressed respecting the truth of the modern 
theory of meteors,—that this circumstance of periodicity 
suffices of itself to demonstrate the extra-terrestrial nature 
of these objects. There are no meteorological phenomena 
which recur persistently on August roth and on November 
13th; terrestrial volcanoes are not, then, exceptionally 
active; the moon on those dates may be in any part what- 
ever of her orbit. The one circumstance to which pheno- 
mena recurring on a particular date can be held to point 
is the recurrent passage by the earth of a particular part of 
her orbit on that date. If we picture the earth circling 
around the sun in her wide orbit, once in each year, and 
remember that year after year as she crosses the particular 
point corresponding to August roth, and again as she 
crosses the particular point corresponding to November 13th, 
her air is alive (as it were) with meteors, we at once see 
that this is because she comes across the meteors at those 
stages of her circuit. It is precisely as though a person 
who travelled continually on a certain road, noticed always 
at certain stages some peculiarities, such as heat or damp, 
or the like. He would be certain, after a few experiences of 
the sort, that the phenomenon was local in its nature,— 
peculiar, in fact, to the particular part of the road where it 
