386 



NATURE 



[May 26, 1910 



T/je Comet and its Spectrum. 



M. Coggia, in No. 19 of the Comptes rendtis (May 9, 

 p. 1 165), gives positions for, and descriptions of, the comet 

 for a number of dates between April 16 and May 6. On 

 April 16, 17, and 18 the comet was seen to have a large 

 nucleus, ovoid in shape, but no tail. Seen with the naked 

 eye on April 21, it was of about the third magnitude and 

 yellowish in colour ; telescopically, the enveloping coma 

 showed two jets in posi lion-angle 120°. With the moon 

 nearly full, a 3° tail was seen on April 23, and was 

 bifurcated. On April 26, with the moon at full, a 1° tail 

 was seen, and a telescopic view showed that the nucleus 

 was smaller than formerly, but was extraordinarily brilliant 

 and decidedly stellar. May 5 found the comet as a second- 

 magnitude object with a tail 10° in length having a curved, 

 plume-like form at its extremity. Seen in the telescope, 

 the nucleus was round and very bright, and was sur- 

 rounded by a coma containing two aigrettes. These were 

 broad and w-ere symmetrical with regard to the nucleus, 

 from which they emerged in directions perpendicular to 

 the axis of the tail. On May 6 the nucleus was yet 

 brighter, and the aigrettes had disappeared, but there was 

 a very bright sector turned towards the sun. 



A circular from Kiel announces that observations at the 

 Lick Observatory, on May 20, showed the length of the tail 

 to be 140°, that is to say that, were it all visible, it 

 would traverse more than three-quarters of the visible 

 hemisphere. The observations were made in the morning 

 in the eastern sky, and showed the tail to lag far behind 

 the radius vector, so it was suggested that the earth would 

 not pass through it. On the morning of May 21 the tail 

 was fainter, but was traced to beyond Aquila. 



A correspondent, Mr. E. Clegg, at Morenas, near 

 Pernambuco, reports that during the early days of this 

 month the comet was seen very plainly at about 4 o'clock 

 each morning by a number of people. 



Despite the smoke and cloud near the horizon, and the 

 full moon, the comet was seen as a conspicuous object by 

 thousands of people in various pafts of the country on 

 Sunda)" evening last. At Gunnersbury it was first picked 

 up at 8.45, although the sky was by no means dark, but, 

 probably owing to the bright moonlight, the tail was only 

 suspected. Mr. W. E. Rolston reports that, to the naked 

 eye, it appeared as a white, nebulous cloud, of appreciable 

 size, having a bright centre. By averted vision 2° or 3° 

 of the tail was glimpsed at intervals. 



The results of a number of spectrum observations, made 

 at the Meudon Observatory during the period January- 

 May, are published, by MM. Bernard and Idrac, in No. 19 

 of the Comptes rendus. In January the cvanogen band at 

 X 388 dominated the spectrum of the head. The photo- 

 graphs obtained on February 9 and March 2, 3, and 4 

 show, in addition, the blue " carbon " band at \ 474 and 

 others, more feebly, near A 408 and X 438 ; in the later 

 spectra the bands at A 388 and A 474 were nearly equal 

 in intensity. A visual observation by M. Giacobini on 

 .'\pril 17 showed the nucleus to be stellar in character with 

 a circular nebulosity surrounding it, but to the Meudon 

 observers on April 25 the condensation was planetary in 

 character, with uniform luminosity over a circle some 5" 

 in diameter. .\ nebulosity of 30' diameter surrounded it, 

 and showed two short jets on the opposite side to the 

 sun. Photographs taken on .April 26 showed that the tail 

 was developing in the form of two jets about 1° in length 

 separated by an angle of some 8° or 12°. 



Spectrograms obtained on .\pril 26 showed only the band 

 at A 474, but others, secured on May 4, showed the con- 

 tinuous spectrum of the nucleus, and, in the head, the 

 bands at A 474 and A 388. It is interesting to note that, 

 probably owing to the differential absorption of the earth's 

 atmosphere at a low altitude, the band at A 388 was much 

 fainter than that at A 474. 



On May 7 the comet was much brighter, its estimated 

 magnitude being 05, and a tail 1° long was easily seen 

 with the naked eye. The head of the comet exhibited 

 several modifications, the nucleus now being elongated in 

 the direction perpendicular to the sun-comet line, and 

 having a luminous jet at each extremitv of its major axis. 

 Spectra, taken on 2 and Wratten and Wainwright's ortho- 

 chromatic plates, show the intense continuous spectrum of 



NO. 2 1 17, VOL. 83] 



the nucleus extending from A bbo to A 395. The band at 

 A 474 is very intense in the spectrum of the head, which 

 also shows condensations at AA 51b and 563 ; the cyanogen 

 band at A 388 is much weaker than on the earlier 

 plates. ... 



Messrs. \'. M. Slipher and Lampland also give a good 

 preliminary account of the comet and its spectrum in 

 Bulletin 47 of the Lowell Observatory. 



Photographs were secured on every morning between 

 .April 14 and May i inclusive, except .April 28, and indicated 

 some remarkable changes in the form of the comet. On 

 .April 30 it was seen that the bilateral symmetry of the 

 earlier photographs of the tail had disappeared ; the 

 northern edge was now nebulous, whilst the southern was 

 bright, well defined, and showed several sharp bends. On 

 May I the tail was gently curved, first to the north, then 

 to the south, for seven degrees from the head, and then 

 became nebulous, with a number of brighter condensa- 

 tions. This outer part indicates the- action of some 

 shattering, perturbative agency, and the proximity of Venus 

 is tentatively suggested as a possible cause. The lengths 

 of the tail, shown on the photographs, range from 1° on 

 .April 15 to i8^° on May i. 



The photographic spectra cover the whole range from the 

 red to the ultra-violet, and show many interesting features. 

 One of the most striking is the intensity of the continuous 

 spectrum of the nucleus, the solar origin of which is 

 indicated by the presence of many Fraunhofer lines. More 

 than a dozen emission bands were photographed, the 

 typical cometary bands 3883, 4737, 5165, and 5635 being 

 generally the most prominent. The cyanogen band at 

 A 3883 is the strongest, and shows progressive intensifica- 

 tion. Other notable bands are at A 4000, prominent in 

 tail; 4214, strong and increasing; 426, prominent in tail; 

 455, apparently composite, and prominent in tail; 570, 

 faint and narrow ; 5893, sodium (emission) lines, varying 

 in intensity; 630+ ; the continuous band is photographed 

 to a short distance beyond B. The study of the sodium 

 lines from day to day indicated that they fluctuated in 

 inienGit}'. 



The objective-prism photographs show that the head and 

 tail are not alike in composition, a point brought out in 

 the studv of Morehouse's comet. Two bands, in fact, at 

 AA 4000 and 4260, were first recognised in the tail; 4550 

 is also prominent in the tail, but inconspicuous in the 

 head. The cyanogen bands at AA 4214 and 3883 are prac- 

 tically absent from the tail. 



Other observations of the comet are recorded by M. 

 Esclangon and M. Borrelly in No. 20 of the Comptes 

 rendus (May 17). 



While visual obse-vations show the tail as straight and 

 bifurcated, photographs show it to be more of the intricate 

 form exhibited on photographs of Morehouse's comet. 

 According to the Times, a splendid photograph was secured 

 bv Mr. Evershed, with the 9-inch reflector at the 

 Kodaikanal Observatory, on April 22. This shows the 

 nucleus as surrounded by a parabolic envelope, from which 

 radiate a number of streamers in the form of a fan. 

 Instead of the simple bifurcated extension seen visually, 

 this photograph represents the tail as a rilimber of dis- 

 turbed, bent streamers, one of the brightest of which 

 actually crosses the others. The photograph certainly 

 suggests energetic disruptive action rather than a steady 

 streaming forth, and demonstrates the danger of com- 

 paring modern photographic representations of comets with 

 the earlier drawings. 



An excellent series of photographs has also been secured 

 at the Helwan Observatory, and copies forwarded to the 

 Roval Astronomical Society. 



The complicated structure of the tail is also shown on 

 photographs taken at the Transvaal Observatory on- 

 April 16. Describing them in No. 441 1 of the Astro- 

 nomische Xachrichten, Mr. Innes says that they show a 

 tail 3° long, divided into five rays, one set of which cross 

 over the others. In the telescope, on the same date,, the 

 nucleus was seen to be double, the secondary nucleus being 

 in position-angle 48° 11'. No. 4413 of the Astronomische 

 Nachrichten also contains numerous reports of observa- 

 tions of the comet. 



The following is part of an ephemeris published by Dr. 

 Ebell in No. 4411 of the Astronomische Nachrichten : — 



