PROGRESS OF METEORIC ASTRONOMY 451 



tions of motion to that of the Perseids, but more evidence is 

 required. The shower is brief and its meteors often few ; and 

 the difficulty in deriving the exact position of the radiant point 

 from night to night is considerable. 



Another feature of meteor streams which has received ample 

 recognition in recent years is the apparently very long duration 

 of many showers from a fixed or stationary radiant. Theore- 

 tically the radiant should show a displacement from night 

 to night similarly to the Perseids and Lyrids. But Greg 

 found many showers which seemingly continued a long period. 

 Some of them were suspected to change their places some- 

 what, and a proportion of them apparently advanced in R.A. 

 with the time. 



The writer made many observations at Bristol in 1876 

 and following years ; one notable outcome of his watching 

 was that a great majority of the secondary meteor streams 

 are visible during an abnormal length of time, and that 

 no variation whatever takes place in the position of the 

 radiant amongst the stars. Certain showers appear to be 

 maintained for as long a period as six months, and instances 

 were not wanting in which radiants continued in active play 

 all the year round ! It is true that meteors were not remarked 

 emanating from these points on every night of the year ; but 

 they would be noticed at intervals — proving that there was at 

 least an intermittent discharge, if not an absolutely continuous 

 one. And the curious point was that the radiant remained 

 precisely in the same position, allowing for slight and un- 

 avoidable errors attending observation. Thus there are dis- 

 plays of meteors from about i6i° + 59°, 262° + 62 , and 3io°-f79° 

 in the Spring, Summer, Autumn and Winter ; and I believe 

 that with man}' additional observations the three showers named 

 and many others would be found continuous or nearly so. 

 The ordinary meteoric displays are however so exceedingly 

 feeble that it is hard to define either their beginning or ending ; 

 and an observer — after perhaps 30 or 40 hours of careful 

 watching within the same week — will find he has not recorded 

 a sufficient number of tracks to indicate some of the radiants 

 with precision. Yet as a rule five tracks are enough for the 

 purpose. Such is the attenuated state of certain systems, how- 

 ever, that they do not provide one meteor in ten hours to the 

 region of sky commanded by one observer. 



