224 



NATURE 



[April 21, 1910 



On May 20 the distance of the comet from the earth 

 yy'xW be about fourteen million miles, but by May 30 

 this distance will have increased to more than forty 

 million miles. 



The two diagrams here given show, roughly, the 

 conditions of observation, Fig. i for the eastern appari- 

 tion, Fig. 2 for the western. In Fig. i the stars are 

 shown approximately as they appear to an observer 

 in London looking due E. one hour before sunrise 

 <i.e. 3.30 a.m.) on May i ; the dated circles represent 



Fig. I. 



the approximate positions of the comet for the date 

 given. Unless the eastern sky is fairly clear it is 

 questionable whether Venus will be seen. It is 

 obvious that to see the comet during its period as a 

 "morning star" one niust get away from the smoke- 

 laden horizon found near large towns, and ascend to 

 as great an altitude as possible. The observation will 

 probably not be a simple one, for at this time of the 

 year the sky, an hour or so before sunrise, is never 

 dark unless cloudy ; the dawn comes quite early. For 



this morning apparition, the , 



Great Square of Pegasus should 



act as a splendid " warner " and 



landmark, just as it did in the 



evening apparition of comet 

 1910a. This mutual association 



of the two comets with Pegasus 



affords a good example of one of 



the chief difficulties experienced 



bv those astronomers who have 



endeavoured to trace Halley's 



comet amid the mass of brief and 



verv general records of comets in 



ancient chronicles. Fig. 2 illus- 

 trates the conditions after Ma: 



20, when the comet will be an 



evening star; the observer is 



supposed to be looking due \V. 



at one hour after sunset on Ma\ 

 25 (about 9 p.m.) ; with a clear 



horizon, Procyon may serve as 



the indicator, but in any case 



Gemini and Leo will afford ready landmarks. It is 

 now the general opinion, and hope, that no chart will 

 be necessary during the last week or so in May, 

 for the comet gives indications that it will probably 

 be bright enough to be seen without difTiculty. One 

 favourable point is, of course, that during the morning 

 apparitions the tail will rise before the comet, whilst 

 under the conditions shown in Fig. 2 it will set later. 

 That the comet has developed a tail of some size is 

 shown by photographs taken at Juvisy on February 



NO. 21 12, VOL. 83] 



12 and at Ottawa on February 10. The former show 

 a thin, feeble tail 1° 30' long, the latter, which i 

 reproduced in Fig. 3, a tail ^° long. From M 

 Baldet's drawing, made at the Juvisy equatorial 01 

 March 5, it would appear that the southern brand 

 shown by him. Fig. 4, was probably too faint t( 

 impress itself on the Juvisy photograph. It is inter 

 esting to recall, here, that" in the 1835 apparition th 

 comet, for some time after passing perihelion (Novem 

 ber 16), showed no trace of the tail, which on Octobe 

 15 had extended to a distance o 

 20°. . According to Sir Johi 

 Herschel in his " Outlines o 

 Astronomy," the comet was no 

 picked up, after perihelion, unti 

 January 24, 1836, and then pre 

 sented a small, round, well-de 

 fined disc, rather more than 2' ii 

 diameter. 



According to a correspondent o 

 the Morning Post, the comet wa: 

 seen at Greenwich Observatorv 

 as a nebulous disc, some 30" ii 

 diameter, in the lo-inch tele 

 scope, on the morning of Apri 

 18. A nucleus, from 3" to 5 

 in diameter, was recognised, bu 

 no definite tail could be seen 

 probably on account of the ap 

 proaching daylight ; there wa = 

 however, a lack of definition, 01 

 the western side of the head 

 probably denoting the presence of the tail. With th' 

 13-inch telescope the comet was followed until 4.2, 

 a.m., and was estimated to be as bright as a secon< 

 or third magnitude star. 



While the chance of capturing a sample of thi 

 comet, as suggested by Dr. Allen, is perhaps ver 

 small, it is a pity that apparently no action is beinj 

 taken. The passage of the earth through a comet'; 

 tail is so rare an occurrence that even a small oppor 

 tunity ought not to be missed. In the April numbe 



Fig. 2. 



of the Bulletin de la Societe Astronomique de France, 

 M. C. E. Guillaume suggests the liquefaction of a 

 large quantity of air which could afterwards be 

 treated by fractional distillation, and possibly some 

 cometary matter recognised. He points out that 

 very minute quantities of the rare gases, e.g. krypton, 

 are thus secured from immense volumes of air, and 

 that it is now possible to liquefy 1000 cubic metres of 

 air per hour; as he remarks, it is just possible 

 that by this means the chemical study of the comet 



