OBSERVATIONS OF LUMINOUS METEORS. 371 



tion. In their orders of magnitudes meteors may thus be distinguished 

 as either — 



I. Telescopic meteors, only rendered visible to the eye by the aid of 

 telescopes ; 

 II. Shooting-stars, visible to the naked eye, and comparable to tho 

 different apparent magnitudes of the fixed stars in bright- 

 ness ; 



III. Bolides and Fireballs, or very luminous meteors, comparable in. 



brilliancy to the planets Jupiter and Venus, and to the dif- 

 ferent phases of the moon, and sometimes even rivalling the 

 sun by appearing with much splendour in broad daylight ; 

 the term Bolides being usually applied to the smaller, and 

 Fireballs to the larger kinds ; 



IV. Detonating, or "Aerolitic" meteors, fireballs which produce an 



audible explosion, like a distant cannon's, a peal of thunder, 

 or an earthquake's shock, by their concussion with the air ; 

 and which differ accordingly from the last (as "forked " light- 

 ning often does from distant or " sheet " lightning) only by the 

 thunderclap that not unfrequently reverberates from fireballs 

 of the largest and brightest class ; or finally as — 

 V. Stonefalls and Ironfalls (the latter very rare occurrences), or the 

 falls of meteorites, either singly or in a shower, it may be, of 

 many thousands of fragments from a fireball, which, especially 

 if seen in the daytime when these occurrences are usually 

 observed, is almost always a large meteor of the last-named 

 description. 

 For each of these different kinds of apparitions it is necessary to 

 furnish separate and somewhat independent directions and instructions 

 to enable good and useful accounts of their phenomena to be pre- 

 served. 



I. Telescopic meteors are not unfrequently noticed during astronomical 

 observations ; and some singular records of the occurrence of such bodies 

 byday and by night in dense showers have been placed on record. The 

 point to which a telescope is directed (in R.A. and Deck), with the hour 

 when such an object presents itself, and its brightness compared with 

 that of fixed stars seen with the same telescope, is to be stated ; and the 

 position-angle of a diameter, or radius of the field of view drawn parallel 

 to the direction toivards which the meteor shot should be determined in 

 the degrees or quadrants usually adopted by astronomers (making the 

 allowance for inversion of the image which the telescope requires) with 

 as much precision as can been ensured. The length of path, if not pro- 

 longed beyond the view of the telescope, can be stated by comparison 

 with the known width of its field in minutes or parts of a degree of arc ; 

 and deviations of straightness, change of brightness and appearance . of 

 the head, during its passage, as well as the persistence on its track of a 

 fitreak or of sparks, if visibly remaining, should be noted, with the 

 duration in seconds, as nearly as it can be estimated, of the meteor's 

 flight while the nucleus was in sight. A streak will often mark the line 

 of passage of a meteor which crosses the field of view too swiftly to be 

 followed with the eye, and the breadth of this light-streak in minutes or 

 seconds of arc should then be noted, with its brightness and duration, 

 appearance and changes of appearance, and with the magnifying power 

 of the telescope employed. A star spectroscope should also be used 



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