ASTRONOMICAL PHENOMENA AND PROGRESS. 



2. The first comet of 1819 ia regarded by Dr. 

 Weiss as a probable member of the Bida group. 

 This body, discovered by Pons, was visible only 

 four days. Its elements, as computed by Poison, 

 have a s'trikinfr resemblance to those of Biela's com- 

 et, the longitudes of the ascending nodes differing 

 by only 1. There can be little doubt that it was 

 connected, in its origin, with the comet of Biela. 



8. The companion of Biela, observed in 1846 and 

 1852, is another comet of the same cluster. The 

 fact that several cometary masses move in orbits al- 

 most identical, may afford a plausible explanation 

 of the division of Biela's comet. Was one member 

 of the group overtaken by another as they were ap- 

 proaching perihelion in 1845, and was their separa- 

 tion after imperfect collision the phenomenon ob- 

 served at that epoch ? 



4. The comet detected by Pogson, at Madras, on 

 December 2 and 8, 1872, mav nave been another 

 member of the same family. Its perihelion passage 

 occurred nearly three months after the time com- 

 puted for that of Biela. Prof. Newton has re- 

 marked that so great a lengthening of the period 

 could not probably be explained by planetary per- 

 turbation. 



M. lloek has shown that certain comets have 

 been associated in groups before entering the solar 

 domain. When the members of such cometary sys- 

 tems are widely separated, thev may pass round the 

 sun in very different orbits. The comets, however 

 which constitute the Biela cluster must have entered 

 our system at small distances from each other, since 

 their orbits are nearly coincident. These orbits, 

 l>itween longitude 255" and 265, pass within no 

 great distance of that of Jupiter. The group had 

 perhaps made its first perihelion passage in a para- 

 bolic orbit. Receding from the sun, It fell under 

 the controlling influence of Jupiter ; the comets had 

 various positions in relation to the planet, and hence 

 the orbits resulting from the attraction of the latter 

 were slightly different. 



We mifflit regard the comet of 1772 the compan- 

 ion of Biela, and Pogson's comet of 1872 as prob- 

 ably identical, but for the small increase of distance 

 between the two Biela-comcts in the interval from 

 1846 to 1852. The period would be about 2,45C days. 



The author argues that the comets of this 

 cluster have been moving in their present or- 

 bits hut a comparatively short time this being 

 rendered probable by the fact that no two 

 members hitherto detected have become wide- 

 ly separated, and that, notwithstanding the 

 frequency of the return to perihelion, the me- 

 teoric debrit is much less diffused than in the 

 case of other known streams. 



Knfke 1 ! Comet. Reports of Profs. ITall and 

 Iliirkness on observations of Encke's com- 

 et, during its return in 1871, are published 

 as an appendix to a volume from the United 

 States Naval Observatory. Prof. Ilarkness 

 (rives his views of the spectrum of the comet, 

 followed by discussions of the probable mass 

 f>t' the comet, find the density of the supposed 

 resisting medium of space. The following are 

 his general conclusions: 



1 . Encke's comet gives a carbon-spectrum. 



2. From November 18th to December 2d 

 the wave-length of the brightest part of the 

 second band of the comet's spectrum was con 

 timmllv increasing. 



8. No polarization was detected in the light 

 of the comet. 



4. The mass of Encke's comet is certainly 

 not less than that of an asteroid. 



5. The density of the supposed resisting 

 medium in space, as computed from the ob- 

 served retardation of Encke's comet, is such 

 that it would support a column of mercury 



220 . 285 , 

 somewhere between-,,- and -^s of an 



10" 



10 W 



high. 



6. There is some probability that the elec- 

 tric currents which give rise to auroras are 

 propagated in a medium which pervades all 

 space, and that the spectrum of the aurora is, 

 in reality, the spectrum in that medium. 



7. It is not improbable that the tails of all 

 large comets will be found to give spectra 

 similar to that of the aurora, although addi- 

 tional lines may be present. 



Other Comets. On the 3d of April, M. 

 Stephan, at Marseilles, found the comet of 

 1867, originally discovered by Tempel, a comet 

 of short period. It had been close to the planet 

 Jupiter, and its time of perihelion passage al- 

 tered thereby nearly two months. July 3d, 

 M. Tempel, at Milan, discovered a comet of 

 short period, the elements of which have been 

 calculated by Dr. Schulhof. M. Borelly, of 

 Marseilles, discovered another comet, August 

 20th ; and on the 23d M. Paul Ilenry, at Paris, 

 reported still another. These were all faint 

 telescopic objects. M. Stephen obtained an 

 observation of Faye's comet, September 8d; 

 it was still exceedingly small nnd faint, and 

 only about 9" from its computed place. Dr. 

 Vogel, of Bothkamp, has observed the spectra 

 of Borelly's and Henry's comets. The spec- 

 trum of the first named consisted of three 

 bands in the yellow, green, and blue. The rel- 

 ative intensity of the bands in order from the 

 red was indicated by the numbers 8. 7, and 2. 

 Each of the bands shaded off very markedly 

 from toward the violet, the greatest intensity 

 being toward the red. Only one observation 

 was made, and then the comet wns near the 

 horizon. The spectrum of the other comet 

 consisted of three ordinary bright lines, which 

 were, however, sharper than usual toward the 

 red. Some of the bands bear a clear resem- 

 blance to the carbon-spectra. 



Telescopic Olservation ofjtfeteort. Dr. Galle, 

 of Breslnu, maintains the theory that multiple 

 meteors enter our atmosphere in flights, and 

 do not owe their separation into discrete 

 bodies to the effect of explosion. Recently, 

 Dr. Reimann observed with the Konigsberg 

 heliometer three small meteors traversing the 

 field, separated from each other by small dark 

 spaces. The two in front were smaller than 

 the third, and the three presented the appear- 

 ance of an isosceles triangle. These bodies 

 moved so slowly that they could be conven- 

 iently watched. The slow motion implies 

 great distances; yet they were as bright as 

 stars of the fourth magnitude. The bodies 

 showed no trains. 



In another case Dr. Reimann observed a 

 small meteor, and a fainter meteor following, 

 about a quarter of a degree distant. Another 



