_Differences of Motion._—Great differences are observed in the velocity of meteors. An observer may notice all varieties on the same night of observation. Some will move very slowly, others shoot quickly across the sky. These differences are occasioned by the astronomical conditions affecting the position of the meteor-orbit relatively to the motion of the Earth. Thus the meteors of Nov. 13 move with great velocity (44 miles per second), because they come directly from that part of the heavens towards which the Earth is moving; hence the orbital speed of the Earth (18½ miles per second) and meteors (26 miles per second) is combined in the observed effects. But in the case of the meteor-shower of Nov. 27 the motions are extremely slow (about 10 miles per second), as the Earth and the meteors are travelling nearly parallel in the same direction, and the latter have to overtake the Earth. _Nomenclature of Meteor-Systems._—It is customary to name the showers after the constellation from which the meteors appear to diverge. Thus the meteors of April 20 are called _Lyrids_, the radiant being in Lyra; the meteors of August 10 are termed _Perseids_, the point of emanation being in Perseus. The two great streams of November are known as the _Leonids_ (13th) and _Andromedes_ (27th). Several showers are often visible in the same constellation; and when it is desired to name these according to the above system, it is necessary to add the approximate star to distinguish them. Thus, in August there are showers of μ Perseids, ε Perseids, and α Perseids, in addition to the well-known Perseids of August 10. _Meteor-Storms._—On Nov. 12, 1799, Humboldt, at Cumana, in South America, saw “thousands of bolides and falling stars succeed each other during four hours.” On Nov. 12, 1833, this shower recurred, and was witnessed with magnificent effect in America. One observer stated that between 4 and 6 A.M. (Nov. 13) about 1000 meteors per minute might have been counted! Another display occurred on Nov. 13, 1866, and on this occasion 8485 meteors were enumerated by several observers at Greenwich. A different system gave us a brilliant exhibition on Nov. 27, 1872, when 33,000 meteors were counted by Denza and his assistants at Moncalieri, in Italy, between the hours of 5^h 50^m and 10^h 30^m P.M. A repetition of this phenomenon occurred on Nov. 27, 1885, when the same observers counted nearly 40,000 meteors between 6^h and 10^h P.M. [Illustration: Fig. 57. VERTICAL. Flight of Telescopic Meteors seen by W. R. Brooks, Nov. 28, 1883.]