January 21, 1909] 



NA TURE 



OUR ASTRONOMICAL COLUMN. 



Periodical Comets due to Return this Year. — In a 

 letter to the Observatory (.No. 405, January, p. jb) Mr. 

 Lynn directs attention to tlic periodical comets which may 

 be re-discovered during the current year. 



Hallcy's comet cannot be reckoned among those of 1909, 

 for its perihelion passage does not take place until next 

 year, but it seems likely that it will be re-discovered, at 

 least photographically, before the present year closes. 



The only short-period comet likely to be re-observed is 

 that generally known as Winnecke's, because he, after re- 

 detecting it in 1858, proved its identity with the object 

 discovered by Pons in 1819. The period is about 55 years, 

 and it was re-observed in 1S69, 1875, 1886, 1892, and i8g8 ; 

 on the latter occasion it passed perihelion on March 20, 

 so it should become observable early this year. In 1880 

 and 1903 it was unfavourably situated, and was not seen. 



The Changes in the Tail of Morehouse's Comet. — 

 In No. 4297 of the Astroiwmische Nachrichten (p. i, 

 Januarv 9) Prof. Max Wolf discusses the forms and 

 motions which successively occurred in the tail of comet 

 igoSc, as shown by measurements of photographs taken 

 at the Heidelberg Observatory. 



Prof. Wolf gives the results of his measures of pairs 

 of photographs taken at definite intervals, and shows that 

 the matter forming the tail appears to have been expelled 

 in waves, these waves being shorter than the similar ones 

 seen in Daniel's comet. The length of these waves appears 

 to be approximately proportional to their distance from 

 the nucleus, whilst their amplitude is still nearer pro- 

 portional to their distance. 



Examined in the stereoscope, these wave-forms take 

 a screw-like appearance, the south-eastern edge of each 

 condensation or cloud appearing to be nearer to the 

 observer than the north-western edge. In general, the 

 measures show that recognisable condensations travelled 

 with a greater velocity as they receded further from the 

 head. 



The Magnetic Field in Sun-spots. — In No. 4, vol. 

 xxviii., of the Astrophysical Journal Prof. Hale publishes 

 a full discussion of the recent work which led him to 

 rj^cognise the existence of powerful magnetic fields in sun- 

 spots. 



-As previously described in Nature (August 20, 1908, 

 No. 2025, p. 368), these fields were demonstrated by the 

 appearance of the Zeeman effect in connection with certain 

 lines in the sun-spot spectrum. Subsequent work has 

 amply confirmed the conclusions then arrived at, and one 

 or two diflficulties have been removed. One of these 

 difficulties was that certain doublets did not appear as 

 triplets even when the spot was as much as 60° from the 

 centre of the sun ; another was that the iron line at 

 \ 6302-71 appeared as an asymmetrical triplet in the spot 

 spectrum, and was accordingly classed as a doublet with 

 an interfering line of some other element. Work on labora- 

 tory spectra, carried out by Dr. King, has, however, 

 shown that these apparent anomalies occur in the terrestrial 

 spectra, and are therefore real phenomena due to the 

 magnetic field. 



The Spectrum of Mars. — The occurrence of the a 

 water-vapour band in the spectrum of Mars, previously 

 reported briefly, is discussed at some length by Mr. 

 Slipher in the December (1908) number of the Astro- 

 physical Journal (vol. xxviii., No. 5, p. 397), and illus- 

 trated by reproductions of the convincing spectra obtained 

 by the author at the Lowell Observatory. 



Previous investigators of the question of water-vapour 

 bands in the Martian spectra have been at a loss because, 

 whilst visual observations were necessarily unconvincing, 

 photographic observations of the most suitable region of 

 the spectrum, the a band, were very diflficult. Mr. Slipher 

 used especially bathed plates, which gave good spectra 

 of this region, and by taking a comparison spectrum of 

 the moon on the same plate, with the altitudes of the 

 planet and the moon approximately the same, he obtained 

 indubitable evidence that water-vapour plays an important 

 part in the planet's absorption. 



The photographs reproduced show the reinforcement of 

 the a band in the spectrum of the " low sun " as com- 



NO. 2047, VOL. 79] 



pared with the " high sun," and then show the strong 

 reinforcement of this band in the spectrum of Mars as 

 compared with that of the moon ; whilst, on the photo- 

 graphs compared, the other lines and bands of the Martian 

 spectrum are generally weaker than they are in the moon, 

 the a band is, without any question, appreciably stronger. 



More observations are necessary before the amount of 

 water-vapour in the planet's atmosphere can be stated, 

 but the results favour the existence of " snow caps " and 

 a moderate temperature rather than " hoar-frost caps " 

 and a low temperature for Mars. 



A Brilliant Meteor. — Mr. P. Evans, of Kettering, 

 reports that he observed a brilliant meteor at that place 

 on January 11. The object appeared at 8h. lom. p.m., 

 its head being very bright, " like burning magnesium," 

 and followed by a tail 10° or 15° long ; Mr. Evans adds 

 that the meteor was seen low down in the west, and 

 travelling in a southerly direction. 



Camelopardalis, Camelopardalus, or Camelopardus ? 

 — Prof. E. C. Pickering devotes Circular No. 146 of the 

 Harvard College Observatory to a discussion of the proper 

 spelling of the name of this constellation, named by 

 Hevelius in 1690, in order that a uniform spelling may be 

 rigidly adopted by astronomers when making references 

 to it. 



After consulting the classical, zoological, and astro- 

 nomical authorities, he concludes that the correct spelling 

 is Camelopardalis. 



REPORT ON AFFORESTATION IN THE 

 UNITED KINGDOM. 

 'T'HE second report (on afforestation) of the Royal Com- 

 ■'■ mission appointed to inquire into and to report on 

 certain questions affecting coast erosion, the reclamatior* 

 of tidal lands, and afforestation in the LTnited Kingdom 

 has just been published as a Blue-book (Cd. 4460, price 

 6d., Wvman and Sons, Ltd., 109 Fetter Lane, E.C.). 



It will be remembered that in March, 1908, the terms 

 of reference of the Royal Commission on Coast Erosion 

 were extended so that the commission should inquire and 

 report " Whether in connection with reclaimed lands or 

 otherwise, it is desirable to make an experiment in 

 afforestation as a means of increasing employment during 

 periods of depression in the labour market, and if so by 

 what authority and under what conditions such experiment 

 should be conducted." 



We propose to discuss the report later, and only give 

 now the summary of the conclusions of the commissioners. 



Summary of Principal Conclusions. 

 (i) The natural conditions of soil and climate in the 

 LInited Kingdom are favourable to the production of high- 

 class commercial timber such as is annually imported into 

 the country in very great quantities. 



(2) The afforestation of suitable lands in the United 

 Kingdom, if undertaken on an adequate scale and in 

 accordance with well-recognised scientific principles, should 

 prove at present prices a sound and remunerative invest- 

 ment. 



(3) In estimating the profits of sylviculture account must, 

 moreover, be taken of two facts, the increasing consump- 

 tion of timber per head of population all over the world, 

 in spite of the introduction of alternative materials, and, 

 further, the exploitation, waste, and destruction by fire of 

 the virgin forests, especially those yielding the more 

 important building timbers. Already a noticeable shortage 

 of timber supply has resulted, as is evidenced by steadily 

 rising prices and depreciating qualities in all markets. It 

 seems impossible to escape from the conclusion that this 

 tendency will be continued and accentuated, and that a 

 steadv and a very considerable rise in prices may be looked 

 for throughout the present century. The security which 

 afforestation offers for investment is therefore likely to be 

 an improving one, with a corresponding increase in profits, 

 but, to avoid all that is speculative, this prospect has been 

 disregarded in framing our estimates. 



(4) The amount of land suitable for afforestation, but 

 not now under timber, in the United Kingdom may roughly 



