PARABOLIC ORBITS OF METEOR STREAMS 461 



positions of the radiants on the maps were measured off to tenths of a 

 degree; frequently two different maps were used on the same night, partly 

 eliminating possible errors of map projection; so far as possible all observers 

 used the same methods in plotting and recording; and finally, the most 

 important rule of all — under no circumstances were meteors seen on 

 different dates or in different years ever combined to secure a radiant. 

 This rule indeed furnishes the first essential step forward in the solution. 

 Because the earth moves forward 1° per day in longitude, while each 

 meteor stream has also its own motion in space, hence it is evident 

 that the radiant for this stream must depend for its apparent position in 

 the sky upon where the orbits of earth and meteor stream intersect. When 

 both are in motion, the apparent radiant (except for a few well-known cases) 

 can not have the same position in the sky for successive nights. 



The reader is referred to Mon. Not. R.A.S., for 1878, vol. 38, p. 115 for 

 an article by G. L. Tupman, to Astr. Nach. for 1879, vol. 93, p. 209 for one 

 by G. von Niessl, and to Bulletin Astr. for 1894, vol. 11, p. 409 for one 

 by M. L. Schulhof, in all of which the question is discussed at length. 

 A later paper by W. H. Pickering, in Ap. J. 29, 365, 1909 shows 

 certain much wider conditions under which he concludes theoretically 

 stationary radiants can exist, provided the data on which he bases his 

 article is correct. This data comes from W. F. Denning' sGeneral Catalogue, 

 Memoirs R.A.S., vol. 53. Therefore to understand the results we must 

 discuss the data. In my former paper, before referred to, on pages 19, 

 22 and 23, a careful analysis of Demiing's conclusions with regard to the 

 Orionids and a-p Perseids was made. It was there shown that for these 

 streams — and the same would in general be true for most of the others 

 given in the General Catalogue — his conclusions for stationary radiation 

 depended mainly upon radiants secured by combining meteors observed 

 on successive dates, anywhere from 2 to 60 nights, and sometimes successive 

 years. Other excellent observers have been influenced into doing the 

 same and hence our meteor catalogues today are filled by many hundreds 

 of fictitious, or at best very rough positions, because the observers would 

 coml)ine the work of many successive dates, totally ignoring the obvious 

 fact that both earth and meteor stream, and hence their intersection point, 

 were all in motion. Given radiants secured thus, and we can prove station- 

 ary radiation or anything else. Further he does not hesitate to combine 

 radiants which lie sometimes as much as 10° from one another into a general 

 group. In an area ten degrees in diameter a radiant could have consider- 

 able motion and still be "fixed," if we put such wide limits to what we choose 

 to call a radiant. In conclusion our results, reduced separately for each 

 date, show almost no evidence of stationary radiation and so far as they 

 go may be considered to disprove its existence. 



