372 bepobt— 1878. 



if possible to observe its spectrum, if it is of sufficient brightness and 

 duration. 



As it has been contended that telescopic meteors are rendered visible 

 by optical power at vastly greater distances from observers than ordinary 

 shooting-stars can be seen, and that their apparent speeds and lengths of 

 path are, under these circumstances, greatly reduced by distance and 

 rendered inferior to those of the majority of meteors, observations of 

 small telescopic meteors with short slow courses, if they occur, should be 

 carefully recorded, in order to determine if they are principally seen at 

 low apparent altitudes, and moderate real heights only, or with equal 

 frequency at all angular altitudes above the horizon, and therefore at all 

 possible heights above the earth's surface to which the use of astronomi- 

 cal telescopes of the highest powers and apertures enables us to extend 

 our sight. 



II. Shooting-stars are observable with a certain frequency on all cloud- 

 less nights. The result of an attentive watch on such occasions to note 

 their frequency by a few hours' observation, especially if in the absence of 

 the moon, is of great value ; but the fitful activities of many meteor 

 showers often combine together to render a rate of frequency concluded 

 from a single hour's observations deceptive and misleading ; and atten- 

 tion must be paid to noting the middle-time of the watch to the nearest 

 quarter of an hour, as upon its lateness in the night, as well as on the 

 season of the year, depends the average horary number which a single 

 observer may expect to see. 



In comparison with that of an evening hour at six o'clock, the 

 number visible in the same morning hour is about double, and nearly as 

 notably greater for a midnight hour in August or September, than for one 

 in February or March. For an average midnight hour in the whole year, 

 Quetelet estimated the horary number visible to one observer in a 

 European station as about six meteors ; and a greater number than 

 twelve or fifteen meteors seen in an hour at an average time of night 

 and season of the year, may be regarded (though not certainly) as indi- 

 cating an active exhibition of some special meteor shower. It is to the 

 prominency which such exceptional phenomena sometimes reach as 

 meteoric spectacles, that the distinction which has arisen between shower 

 meteors and sporadic shooting- stars is entirely owing; and from the 

 partial extent of our present acquaintance with the directions, intensities, 

 and durations of multitudes of weaker descriptions of such showers, in- 

 numerable shooting-stars must still be regarded as " sporadic " until well- 

 determined centres from which they appear to diverge accurately can 

 be definitely assigned to them. 



To note and reduce shower meteors to their radiant-points is a task of 

 little difficulty to an observer already conversant with the positions of the 

 principal fixed stars, and of the constellations. But the use of star charts 

 properly adapted for projecting meteor- paths soon familiarises unpractised 

 observers with this preliminary preparation ; and facility is soon acquired 

 in drawing upon a map the initial and end-points of a meteor's track, and 

 in prolonging through these points a straight line backwards on the 

 map, or tracing, to show by a simple inspection of a number of these 

 lines their common crossing point, or the focus of emanation of the meteor 

 shower that they belong to, in the sky. The natural impressions of 

 direction are of slender use in endeavouring to fix this point correctly by 

 the eye alone, retracing the meteor's track among the stars themselves ; a 



