May 1, 1891. 



K N O WL EDGE 



95 



K.i'iiiiijjU' 3. — Eichard II. resigned bis crown on Monday, 

 29th September 1399. Test this. 

 1399 

 849 



1748 

 9 



7)1739 



248 -1-3 = Tuesday = 30tb September. 



Thus the 29th September was Monday. 



Many useful minor rules might be added, but intelHgent 

 readers can form these for themselves ; and all interested 

 in the subject of " dutrs " should provide themselves with 

 the invaluable work mentioned above. 



STATIONARY OR LONG-EXDURING RADIANTS OF 

 METEORS. 



To the Editor of Knowxedge. 



Dear Sir, — Although the readers of Knowledge are 

 already aware of the existence of Stationary or Long- 

 Enduring Radiants of Meteors, they are not, perhaps, 

 fully acquainted with the evidence in their favour, or of 

 the difficulties which arise in attempting to explain 

 them. 



The evidence in favour of such long-enduring radiants 

 will, I think, appear conclusive to anyone who arranges 

 the observations comprised in a long catalogue, like that 

 of Mr. Denning in the Monthly Notices of the Royal 

 Astronomical Society for May 1890, in order of Eight 

 Ascension instead of date. 1 have done this with a con- 

 siderable number of catalogues, which generally confirm 

 each other. The force of this kind of evidence may be 

 illustrated by analysing the radiants in Mr. Denning's 

 Catalogue situated between R.A. 2G0'^ and R.A. 270° (the 

 sign + indicating Northern, and the sign — Southern 

 Declination). Here is a complete list of them : — 

 200 '+ 2° Apr. 19. 

 200° 4- 33° Apr. 18. 

 260° -h 45° Jan. 14,17. 

 200° -I- 02° Apr. 19, 26. 

 260 '-I- 63° Sept. 5, 15. 

 260° -I- 68° July 24. 

 260° -I- 09° July 27, 29. 

 261°+ 4° Feb. 15, 20. 

 261°+ 5° June 3, 13. 

 201°+ 63° Jan. 19, 25. 

 202"+ 04° May 11, 14. 

 202°+ 04° June 9,13. 

 262°+ 64° Oct. 5, 12. 

 263°+ 36° Feb. 20, 21. 

 263"+ 48° Mar. 14. 

 263°+ 61° July 29, Aug. 2. 

 263°+ 62° Mar. 28. 

 263°+ 62° Apr. 20, 22. 



Six of these are determinations of the nidiant of the 

 Lyrids (April lH-20) in dill'erent years, but the occur- 

 rence of a radiant near the same point in February 

 suggests a doubt as to whether even this radiant is of very 

 brief duration. One half of the entire number appear to 

 belong to a radiant situated between + 60° and + 70°, 

 which continues active almost throughout the year. Five 

 others belong to a radiant situated between + 45° and 

 + 50°, and three to a radiant between 0° and 5°. The 

 pair at + 20° and +21° are also probably connected ; and 

 the isolated radiants are thus reduced to two, one at +77" 



203°+ 09° Aug. 21, 23. 

 264°+ 62° Aug. 14, 23. 

 204°+ 64° Apr. 30, May 8. 

 264°+ 04° May 28, 30. 

 205°+ 77° Apr. 26, May 3. 

 200°+ 33° Apr. 18. 

 200°+ 47° Aug. 22. 

 260°+ 03° July 13. 

 207°+ 70° Sept. 4, 7. 

 207°+ 21° Apr. 19. 

 207°+ 49' July 15, 20. 

 208°- 24° June 10, 20. 

 208°+ 33" Apr. 19. 

 209°+ 31° Apr. 19. 

 209°+ 33° Apr. 20. 

 269°+ 37° Apr. Ki, 19. 

 269°+ 49° July 20, 31. 



and the other at — 24°. The failure to trace the latter 

 radiant at other times of the year probably arises from its 

 great Southern Declination ; and we thus seem led to the 

 conclusion, not merely that stationary radiants exist, but 

 that they are the rule — a conclusion which, I believe, 

 further analysis of published observations wiU only tend 

 to confirm. 



About a quarter of a century ago the close correspon- 

 dence between certain meteor-showers and the orbits of 

 certain comets was ascertained, and since then the come- 

 tary character of meteor-showers has been generally 

 assumed. Difficulties arise at once when we endeavour to 

 combine this cometary character of the showers with the 

 fact of stationary radiation. We can only fall in with a 

 cometary shower when the earth is at a moderate distance 

 from the comet's orbit, and if this orbit has a high in- 

 cUnation to the ecliptic, the corresponding shower can only 

 be encountered when the earth is near the node. High 

 inclinations, however, predominate among the comets (if 

 we except the comparatively small class of comets of short 

 period), and in the case of the comet which has been 

 connected with the August Perseid shower the inclination 

 exceeds 60°. But that the activity of this radiant is not 

 limited to the month of August appears certain. Thus, 

 Mr. Denning, on reducing the Italian observations of 

 1872, found that it had continued active (though with 

 diminished intensity) during the last five montlis of the 

 year. Reverting to our table, the radiant situated at 

 about 263°+ 03^ is not far from the pole of the ecliptic, 

 and therefore, if cometary, would require a high inclina- 

 tion in the corresponding cometary orbit ; but the shower 

 apparently lasts throughout the year. Again, if a come- 

 tary meteor-train was sufficiently difl'use to produce a 

 shower of considerable duration, the radiant point would 

 not be constant but would shift from night to night ; 

 whereas the constancy of the radiant (within the limits of 

 error) is the fact with which we are dealing. Some 

 observers, indeed, believe that they have observed a 

 shifting in certain radiants ; but the instances are few 

 and doubtful, and the amount of observed shifting does 

 not appear to agree well with the cometary theory. 



The Copernican princiiJe, that we perceive relative not 

 absolute motion, is of course applicable to the apparent 

 motions of meteors, and as the fixed stars are so distant 

 as to be practically in the same direction at all periods of 

 the year, the apparent motion of a meteor among the fixed 

 stars will vary with the direction of the earth's motion at 

 the time. Hence when the direction of the earth's motion 

 varies (the velocity being always pretty nearly the same), 

 the apparent position of the radiant must vary, assuming 

 that the meteors still come to us from the same direction. 

 But we have seen that in a great niunber of cases there is 

 no perceptible change in the position of the radiant at 

 ditl'erent periods of the year, and hence arises a ditliculty 

 altogether independent of tlie cometary theory. 



The late .Mr. Proctor's solution of tliis difficulty is 

 known to the readers of KNowi.EiHiK. The amount of the 

 displacement of the apparent radiant depends on the rela- 

 tive velocities of the earth and the meteors, and if the 

 velocities of the meteors is very great compared with that 

 of the earth, the displacement will be very small — and the 

 observations are consistent witli a very small displace- 

 ment. But observation tends to show that meteors 

 coming from stationary radiants do not possess this very 

 high velocity. Few of the showers appear to be as fast 

 as the Leonids, whose velocity has been computed from 

 the corresponding comet at 14 miles per second. Some 

 of them are noted by Mr. Denning as "slow" or "very 

 slow " ; and, what is perhaps the most cpuclusive evidence 



