March 4, 1870.] ^jy [Kirkwood. 



ON THE PERIODS OF CERTAIN METEORIC RINGS. 

 By Daniel Kikkwood. 

 I. The Meteors op Apkil 20Tn. 

 In tlie AstronomiscTie NacJiricMen, No. 1632, Dr. Weiss called attention 

 to the fact that the orbit of the first comet of 1861 very nearly intersects 

 that of the earth, in longitude 210° ; theijoint passed by the latter at the 

 epoch of the April meteoric shower. A relation between the meteors and 

 the comet, similar to that recently detected between the November me- 

 .teors and the comet of 1866, was thus suggested as probable. Is this hy- 

 pothesis in haiTnony with facts ? and if not, are our present data sufficient 

 for determining with any reasonable probability, the true period of the 

 April meteors '? 



Dates of the April Shower. — Professor Newton selects the follow- 

 ing from Quetelet's Catalogue as belonging to this period :* 



1. B. C. 687, 4. A. D. 1093, '4 '5, and '6 



2. " 15, 5. " 1122, '3 



3. A. D. 582, 6. " 1803, 



Period op the First Comet of 1861. — The elements of this body 

 were computed by Oppolzer, who assigned it a period of 415 y-4. Now 

 while it is true that the interval from B. C. 687 to A. D. 1803, is very 

 ne3,rly equal to 6 periods of 415 years, the slightest examination will show 

 that this period does not harmonise with any of the intermediate dates. 

 This fact, then, without further discussion, seems fatal to the hypothesis 

 that the period of the meteors is nearly equal to that of the comet. 



Wliat is the probable period of the ring ?— The showers of 1093 — 6 and 

 1122 — 3 at once suggest a period of from 26 to 80 years. The nodal pas- 

 sage of the densest portion of the ring at the former epoch may be jalaced 

 any where between 1093 and 1096, and that of the latter, in either 1122 or 

 1123. The entire interval from B. C. 687 to A. D. 1803 is 2490 years, or 

 88 periods of 28 y.295 each ; and the known dates are all satisfied by the 

 following scheme : 

 B. C. 687 to B. C. 15.. ..672.000 years=24 periods of 18, OOOy each. 



" 15 to A. D. 582.. ..597.000 " = 21 " 28.429 " 



A. D. 582 to "1093.714... 511. 714 "=18 " 28.429 " 



" 1093.714 to "1122.143.... 28.429 "= 1 " 28.429 " 



" 1122.143 to 1803... 680.857 "=24 " 28.369 " 



These coincidences indicate a period of about 28^f years, corresponding 

 to an ellipse whose major axis is 18.59. Hence the distance of the aphe- 

 lion is very nearly equal to the mean distance of Uranus. It wiU also be 

 observed that the time of revolution, which seems to have been somewhat 

 lengthened about the Christian era, was previously one-third of the period 

 of Uranus. 



II. The Meteors or December 11th — 13th. 

 In the catalogue of Quetelet we find the four following extraordinary 

 displays which belong undoubtedly to this period. Observations made in 



*Silliman's Journal for July, 1S63. 



t Ilerrick assigned a value of 27 years. See Silliman's Journal for April, 1841, p. Sfi.'i. 



