An introduction to astronomy: designed as a text-book for the use of students in college. By Denison Olmsted ...

2Y70 INDuTmourey Si OWVEIRS.
tilme being nearly commensurable with the eartlh's, Cither a
year or half a year, so tlhat for a number of yea rs ill successionI
tlhe two bodies meet near the same part of the eartll's orbit.'It is further cstablished, that the meteors consist of lightt colmbustible matter; that they move wvith great velocities, amoulltit, i l somle instatlces, to not less than that of the eartl in
it.s orIbit, or 10 niles per secondt; that somnle of thlcem larl bodies
of large size, sometimes several thousand feet in diameter-;
that wthen they citer the atmoslphert, tthey rapidly andl powerfully condense tile air before them, and thus elicit the hIat
that sets tlem oln ir'e, as a sparlk is elicited in the air-match,
by being suddenly condensed by mleans of a piston adltl cylinder; and that thley ar1 burnel ul) at a considerable hltiog'ht
above the carth, sometimes not less than 30 miles.
409. Calling the body fromn Wtich the meteors descenldedi
tle " nmeteoric body," it is inferred thatit is a body of great
extent, since, witlIout apparent exIhaustion, it thas been abl}) to
aftord sucll copious showers of meteors at so many difieerent
times; and ll1 nce we regard the part thlat has descended to the
earth only as thile:ctAlreme.p)ortio.s of a. body or collection of
meteors, of ulnknown i extent, existing in the p)lanletary spaces.
Since the Carth fell ill witht tltd meteoric body, ill the salno
part of its orbit for several years ill suiccession, tthe body mllst
either lave remained there whlile the eartll \as performingll its
wlole revolution around tlhe sun, or it must itself 1thace lhtad fa
revolution, as Nwell as the earthtl..N-o body can remain stationary withlin the planletar'y spaces; for, unless attracted to soime
nearer body, it Nwould be drawn directly tow\ard tihe sunll, and
coulll not hlave been encountered by the carthl again ill twhe
same p:t'rt of herl orbit.;Nor can any mode be conceived in
vhtich this event could have hlappiend. so many times in regtular succces;sion, unless the body lhad a revolution of its own
around thle sun. Finally, to have come into contact wvith tlhe
earttt at the san!e l)art of hler orbit, in two or more successive
years, the body nmust ihave a period which is eitlher nearly the
sanme with the earth's period, or some aliquot part of it. No
pleriod will fulfil these conditions, but either a )year or half a
year. Whlich of these is the true period of the meteoric body,
is not fully determined.