Prof. Newton of Yale College, America, who entered into an elaborate investigation of the subject, concluded that the 5 possible periodic times (the earth's being taken as unity) of the meteor-ring were 2 ± Ty!sz5, ±gg!'iy, and Till.", and that of these the fourth, 1— 3-a-'3-5, or 354.62 days, is the actual period of its revolution round the sun, and that, consequently, it has described 34 revolutions while the earth has described 83, the cycle of 34 meteor revolutions differin,„0. from 33 years by only 3.17 days; and in accord ance with this estimate, he calculated its orbit and the approximate extent (seeing the meteor show-er generally occurs in two successive years) of the meteor-group which produces the November showers. His conclusions have, however, been vigorously opposed by other eminent astronomers, such as Prof. Adams (q.v.) and Mr. Alexander Herschel, both of whom hold that the first four of the possible periods given by Prof. Newton are impossible, and that the last, IT 313-F (i.e., that the meteor-ring makes yrig-6- of a solar revolution in a year, and one complete revolution round the sun in 33.25 years), is the correct estimate. If this view be correct, the meteor-group must be so much extended along its ring or orbit as to take more than a year to cross the earth's orbit, and a long time must necessarily elapse before a fair estimate of its extent can be obtained. A periodic time of 331 years, and an orbit which at the same time approaches so near the sun as to intersect that of the earth, indicate a path of great ellipticity, akin to those of the comets; and the idea of the cometary nature of these meteors derives support from two remarkable facts, the one discovered by Schiaparclli of Milan, that this assumed •orbit coincides very nearly with that of the great comet of 1862 (Prof. Adams connects this comet with the August meteors), and the other by C. F. W. Peters of Altona, that it coincides with that of Tempel's comet.
Mr. Alexander Herschel also maintains that the meteors are of recent origin, probably fragments from some Of the great luminous bodies, and that though at present assembled in a comparatively dense group, the difference of their relative velocities will have the effect of gradually distributing them all over the meteoric ring, when a November shower will occur every year. Mr. Herschel also carefully observed 20 meteors with the view of calculating their weight, from the rate of their motion and the amount of heat (as shown by their brightness) evolved in the destruction of their velocity, by the resist ance of the atmosphere, and found their weight to vary from 30 gr. to 7i lbs.
The cause of the luminosity of meteors was long a point in dispute, the two chief suppositions being, that the resistance of the atmosphere to a body das.hing through it at about 30 miles per second, generated so much heat as to produce ignition; while the other was the action of terrestrial magnetism. The point most strongly urged against the first supposition, by the supporters of the second, was, that the height at which meteors were occasionally seen rendered any action of the atmosphere impossible; but as this objection was founded on the purely hypothetical opinion that the atmosphere did not extend more than about 50 m. from the earth's surface, it was not very cogent. This problem was handled by sir John Herschel in an able paper published in the Edinburgh Review (January, 1848), in which he clearly showed that the very high latent heat of the air in the higher and rarer parts of the atmosphere would be sufficient to cause an enor mous development of heat in the event of the air being compressed before a body advanc ing into it with a " planetary" velocity. This opinion is now held by almost all eminent men of science. The enormous heat to which the meteor is thus subject produces incan descence, after which, with more or less facility, according to the nature of the materials of which the meteor is composed, the outer portion becomes liquid, and, by the powpr ful resistance of the air to the meteor's rapid course, is thrown off in a long stream, forming the tail, which, after rapidly losing its velocity, is precipitated to the earth as a fine dust like volcanic ash; while the meteor, thus rapidly and constantly diminishing as it flies along in its headlong course, either becomes wholly dissipated into " tail," falls to the earth, or makes its way out beyond the limits of the earth's atmosphere, and contin ues its course. This supposition of exclusive atmospheric agency also gives a plausible explanation of the phenomenon of meteors " bursting," this being caused by the sudden heating and consequent expansion of the outer part, while the interior was still in the state of intense cold acquired while in interplanetary space.
While astronomers and physicists in general have been thus trying to reduce the phe nomena of meteors to a system, their chemical brethren have not been idle. Pubhe collections of meteoric bodies have been made at Vienna, the British museum,yaris, Berlin; and private ones by Mr. Greg of Manchester, baron Reichenbach in Austria, and prof. Shepard in America; and opportunities have thus been afforded of determining the nature of their composition.