_Radiation of Meteors._—Heis, in Germany, was the pioneer in this branch of practical astronomy. About half a century ago he began systematic observations, and gathered many useful data. Schmidt, at Bonn and Athens, followed his example; and in England Prof. Alexander Herschel and Mr. R. P. Greg devoted themselves to the subject with highly successful results. Their collective labours revealed a large number of well-defined systems of meteors, and enabled them to publish tables of the radiant-points. The investigations were more precise than formerly, and conducted on methods ensuring more accurate and plentiful materials. The radiation of meteors from fixed points in the sky had been observed before in regard to the great display which occurred in November 1833; but the meteors that fell on ordinary nights were regarded as sporadic, until Heis and his immediate successors showed they were reducible to an orderly arrangement and that every one of them had its radiant-point and its origin in a definite meteor-stream. The apparently divergent flights from a common centre are simply due to the effects of perspective on bodies really moving in parallel directions and collected into groups more or less scattered. [Illustration: Fig. 52. Radiation of Meteors (Shower of early Perseids from 32°+53°, July 28-Aug. 1, 1878.)] _Identity of Meteors and Comets._—The mystery concerning these fugitive objects and their vagaries of appearance was not always to remain concealed. Denison Olmsted had, in his work on ‘The Mechanism of the Heavens,’ published in 1850, stated that the constitution of the body to which the meteors of 1833 belonged bore “a strong analogy to comets.” Reichenbach, in 1858, wrote a paper in which it was sought to prove that a comet is a swarm of meteorites. Prof. Kirkwood, in 1861, also concluded that “meteors and meteoric rings are the debris of ancient but now disintegrated comets, whose matter has become distributed around their orbits.” But it remained for Schiaparelli, of Milan, in 1866, to demonstrate the identity of meteoric and cometary systems. Others had reasoned up to it, and observers had amassed many useful observations bearing on the subject; but absolute proof was wanting until Schiaparelli supplied it. He computed elements for a well-known shower of meteors occurring on August 10th, and found the orbit presented a very close resemblance to that of Comet III. 1862; and he detected a similar analogy between the November meteors and Comet I. 1866. The orbit of the April meteors was afterwards shown by Galle and Weiss to agree with the path of Comet I. 1861; and a meteor-shower occurring at the end of November was found to coincide with Biela’s Comet. Facts like these could not be disproved. Comets were thenceforth known to be the parents—the derivative source—of meteors. Thus two important classes of objects became as one, the differences observed being merely those of aspect due to the variable