3«4 



NA TURE 



[May 26, 1910 



OBSERVATIONS OF H ALLEY'S COMET. 



Observations at the Madrid Observatory and Malta. 



"f N a communication which has been received from Dr. 



■*■ V. Iniguez, the director of the Astronomical and 

 Meteorological Observatory of Madrid, a brief account is 

 given of the visual observations of Halley's comet made 

 at that observatory, accompanied, not only with several 

 excellent photographs showing its general appearance, but 

 with a photograph and drawing of the spectrum of the 

 nucleus and tail. 



According to Dr. Iniguez, the nucleus underwent many 

 variations in size, and these changes can be gathered from 

 the following figures which he gives. Thus on .\pril 21 

 it had a diameter of lo* ; on May 5, 7" ; on May 7, 8" ; 

 and on May 10 it was only 5" in diameter. During May 

 the nucleus was comparable with a star of the first 

 magnitude, that of May lo being a little brighter. 



From photographs taken with a doublet of 5 inches 

 aperture, the first view of the comet only indicated a tail 

 a few minutes of arc in length. On April 25 it extended 

 to one degree. On April 28 it was increased to four 

 degrees. By May 5 it had reached a length of ten degrees ; 



Fig. I.— Photograph of Halley's Comet taken at the Madrid Observatory 

 on Mav 11. 



on May 11 its length was thirty degrees, and on May 14 

 it is described as extending about sixty degrees. The 

 accompanying illustration (Fig. i) shows the comet as 

 photographed on May 11, the exposure lasting from 

 2h. 58m. a.m. to 3h. 44m. a.m. official Madrid time. 



On May 7 and 8 the comet was photographed with a 

 prismatic camera, using a Grubb lens of 8 inches aperture 

 and a prism of twenty degrees angle. The photographs 

 obtained displayed a spectrum which was continuous, but 

 crossed by three morrochromatic bands. On May 9 and 10 

 visual observations of the comet's spectrum were also 

 made, and these also indicated a continuous spectrum 

 crossed by three bands. The wave-lengths of the bands in 

 the spectrum of the nucleus are given as 561 \, 510 A., and 

 472 X, while those in the tail are 550 \, 505 A, and 

 461 \. The forms and positions of the bands are given 

 in the accompanying drawing (Fig. 2), which is a repro- 

 duction of that sent by Dr. Iniguez. 



The second communication is from Mr. C. Leach at 

 Malta, dated May 16, who writes : — ^ 



" Enclosed is a sketch of what was seen here between 

 2.45 and 3.15 a.m. of May 13 and 14. The position and 



NO. 21 17, VOL. 83] 



size of comet were easily noted owing to the clear sky. 

 The chief thing noticeable was the great change in posi- 

 tion since May 10, on which date I sent you a sketch of 

 same. The position of the head on May 14 was as shown, 

 forming a rough parallelogram with ^, a of Andromeda 

 and y of Pegasus; in fact, the head was below y to th' 

 extent of the distance o, y. The tail was quite distinct 

 to ^ of Pegasus and y of Aquarius, and just filled the 

 space between them. A star was seen through the tail 

 ai; its extremity. 



" The width of the comet at the head was about one- 

 seventh of side y, a of Pegasus, and the tail about oni - 

 third of same at broadest part, roughly speaking, 2° and 

 5° respectively. By referring to a star-map, I made out 

 the head to be near to e of Pisces, so that the length must 

 have been nearly 45°. 



" We must have been in a very favourable position and 

 have had ideal conditions, as I see Greenwich observa- 

 tions on May 10 make out the tail only 45 minutes. 



" I am sorry I cannot sketch better, but I have a 

 difficulty in representing just the correct degree of light 

 in the tail, which is much fainter after o of Pegasus. 



" The nucleus was equal to o of Andromeda in bright- 

 ness. 



" The reflection of Venus on the sea was splendid. 

 I think there can be no mistake about the length of 

 the tail of the comet being great enough to allow the earth 

 to pass through it, in spite of statements to the contrary. 



"It was seen by several people here; in fact, the 

 general appearance of the comet is summed up exactly in 

 the comparison used by several, ' Just Hke a searchlight 

 from the fort.' It was not- seen on May 15 and 16 owini* 

 to a sirocco haze." 



Mr. Leach's drawing is here reproduced (Fig. 3) on a 



Fig. 2.— Spectrum of Halley's Comet observed at the Madrid Observatory. 



reduced scale, and illustrates very clearly the comet's form 

 and position among the stars. 



Passage between the Sun and Earth. 



The possibility of the mutual interaction of the comet and 

 earth when the former passed directly between the earth 

 and the sun on May 19 aroused great interest. A tele- 

 gram from the Kiel Centralstelle gave the time of the 

 comet's passage across the solar disc as ingress 

 3h. 22-7m. a.m. (G.M.T.), egress 4h. 22'5m. a.m., but, 

 with one exception, all the reports yet to hand state that 

 no trace of the comet was seen during the passage. The 

 exception was at the Munich Observatory, where, accord- 

 ing to Reuter's Berlin correspondent, the observers 

 " succeeded in catching a glimpse of the comet as it passed 

 across the sun's disc"; until official confirmation is forth^ 

 coming, this statement should, we think, be accepted with 

 reserve. At other German observatories no trace of the; 

 comet was seen, and at Munich the sun would not rise 

 until the commencement of the passage; its altitude, 

 therefore, would be very small. 



The greatest hope for detailed observations of the comet 

 during its passage was centred on the Kodaikanal Observa- 

 tory, in southern India, where careful preparations had been 

 made for visual, photographic, and spectroheliographic 

 observations. Inter alia, it was proposed to take photo- 

 graphs with the spectroheliograph, with the primary slit 

 set on one of the strongest cyanogen bands, in the hope 

 that the cometary radiations might thereby become differ- 

 entially intensified in the image, just as the hydrogen or 

 calcium radiations ordinarily are. But, according to a 

 telegram sent by Prof. Michie Smith to the Daily Mail, 



