October i, 190S] 



NATURE 



539 



how much astronomical science has advanced in the 

 interval, and demonstrates the necessity of frequent 

 revision of popular text-books of this character. In 

 some respects the work has already fallen behind — 

 inevitable from the time required to pass such a book 

 throug'h the press — and thouarh an appendix is not a 

 convenient form for supplyina: the most recent informa- 

 tion, it might have been adopted here with advantage. 

 If we may trust the index and a very careful scrutiny 

 of the te.xt, there is no reference to the eighth satellite 

 of Jupiter. On the same grounds we think that justice 

 has not been done to the energy and success with 

 which Prof. Hale has pursued his investigations, and 

 the references to Sir David Gill are meagre. .Mtogether 

 the revision does not seem to have been made with 

 sufficient thoroughness ; there has been too great a 

 reluctance to sacrifice the material prepared for the 

 earlier edition, with the result that the author has 

 retained references to earlier work which has been 

 superseded by the employment of larger means and 

 greater experience. But though one may regret that 

 in some particulars the work might be improved, it 

 still possesses verv high claims to consideration. The 

 main facts are presented in an admirably attractive 

 manner, leaning perhaps, where opportunity offers, to 

 the sensational side ; but nevertheless the description 

 is trustworthy, likely to captivate the amateur, and 

 gain recruits to the study of astronomy. 



The book is divided into two parts, the first devoted 

 to purelv descriptive astronomy, the other to explain- 

 ing the motion of the heavenly bodies. In the first 

 part, after an introduction explaining the optical prin- 

 ciples of the telescope and its application to photo- 

 graphv and spectrum analysis, we have a series of 

 chapters describing the several members of the solar 

 system, including comets and meteors, and finally 

 the sun itself. Next follows a description of the 

 stellar universe, separate chapters being assigned to 

 the classification of stellar spectra ; the nebula; and 

 star clusters; the Milkv ^^'ay ; double and variable 

 stars. In this section the author's task is compara- 

 tivelv simple. No material fact must be omitted; but 

 in the second part, that treating of motion, he has 

 to exercise selection, both of the subject itself and its 

 method of treatment. Mathematical completeness is 

 impossible, and therefore the chapters on planetary 

 motion, solar parallax, aberration and precession, 

 are scarcely satisfactory. But readers for whom the 

 book is intended will no doubt find the treatment 

 adequate, and those who desire a more thorough dis- 

 cussion would not look for it here. 



Practical Coal Mining. By Leading Experts in 

 Mining and Engineering. Edited by W. S. Boulton. 

 Divisional-volume v. Pp. \'\u+iy6. (London: The 

 Gresham Publishing Company, n.d.) Price 6s. net. 

 In Nature of May 23, 1907, and of March 19, 190S, 

 notices were published of previous instalments of this 

 work, which, when completed in six volumes, is in- 

 tended to cover the whole ground of modern coal- 

 mining practice. Each section of the work is written 

 bv a different author, a division of responsibility that 

 renders a certain want of harmony in the treatment 

 of the subject-matter inevitable. This defect is less 

 noticeable in the present volume than in the four pre- 

 ceding volumes. Mr. James Ashworth's contribution on 

 lighting covers 56 pages, with 125 excellent illustra- 

 tions, and gives a concise review of the history of the 

 safetv lamp, and of the safety lamps in use at the 

 present day. The importance of lamp housing is 

 urged, and useful rules are given for the use of safety 

 lamps. Mr. W. Galloway devotes 70 pages with 30 

 illustrations to a masterly essay on colliery explosions 

 and rescue appliances. This contribution is also issued 

 separately by the publishers. The subjects of fire damp, 



NO. 2031, VOL. 78] 



blasting, coal dust and rescue appliances are fully 

 discussed. Mr. Galloway's new departure in the 

 method of explaining great colliery explosions whereby 

 coal-dust is elevated to the rank of principal agent was 

 received unfavourablv and long rejected by many as 

 illusory. Now, even the French engineers, after the 

 Courrieres explosion, have come into line with those 

 of other countries, after having strenuously opnosed 

 the so-called coal-dust theory for thirty years. Mr. 

 H F. Bulman gives a brief account of mineral hold- 

 ings, covering 20 pages. Lastly, there is the be- 

 ginning of what promises to be a most useful section 

 on mine surveying by Mr. L. H. Cooke. 



LETTERS TO THE EDITOR. 

 [The Editor does not hold hii)isclf rcsponsiblw for opinions 

 expressed by his correspondents. Neitlier can he nndertalte 

 to return, or to correspond with the writers of, rejected 

 manuscripts intended for this or any other part 0/ Nature. 

 No notice is taken of anonymous communications.] 



Photographs of Comet , 1908 at the Royal Observatory, 

 Greenwich. 



Long-exposure photographs of comet c 1908 have been 

 obtained with the 30-inch reflector on September 6, 7, 8, 

 14, 17, 18, 21, 25, and 26, the e.xposure ranging from forty- 

 five minutes to an hour (except on September 14 and 25, 

 when exposures of twenty minutes were made). The comet 

 possesses a bright tail,' the structure of which is well 

 shown in the photographs, to a distance of li" from the 

 head. The appearance of the tail changes greatly from 

 night to night, so that photographs taken at much shorter 

 intervals than a day are desirable in order to trace _ the 

 alterations in structure continuously. With this in view, 

 on September 17 three photographs, with exposures of 

 forty-five minutes, were taken at intervals of approximately 

 an hour (reckoned from the middle of each exposure) ; 

 decided change had occurred between the first and last 

 photographs, and the middle photograph served to show 

 how 'the transition had taken place. Efforts are being 

 made to obtain a series of photographs at short intervals 

 extending throughout a night, but so far the full moon 

 and the weather have prevented this. 



A photograph taken on September 21 with a portrait 

 lens of II inches focus showed the tail extending to a 

 length of 4°. '^^'- "■ ^^- Christie. 



Royal Observatory, Greenwich, September 28. 



Library Cooperation in Regard to Scientific Serials. 



About two years and a half ago a short paper of mine 

 on " Library Aids to Mathematical Research " was for- 

 tunate enough to attract a little passing attention, the 

 object of it being to bring about friendly cooperation among 

 the public libraries of a city or district with a view to 

 prevent waste in the purchase of duplicates, and thereby 

 to make a greater number of serials accessible to research 

 students. Of course, it was intended that this cooperation 

 should be accompanied by the publication of a hand-list 

 giving the names of the serials, and showing workers in 

 what libraries any given serial was certain to be found. 

 In Nature in particular the matter received sympathetic 

 consideration (see vol. Ixxiii., pp. 372, 413 J38, 464, 513), and 

 from the eminence of the correspondents hopes were raised 

 that something practically valuable would be the outcome. 



In the matter of voluntary cooperation among the 

 libraries, exceedingly little would seem to have been 

 effected,' and the place where the need is greatest, London, 

 appears to be as far off as ever from possessing a reference- 

 library in which could be consulted the whole of the litera- 

 ture indexed in the Royal Society's Catalogue of Scientific 

 Papers and in the International Catalogue. 



.As regards the production of a hand-list of serials, how- 

 ever, a most important step has been taken, the Royal 

 Societv having decided to preface each volume of its great 

 subject-index with such a hand-list, and having actually 

 carried out its decision in the case of the first volume. 

 In this volume, which has recently appeared, and in which 

 the pure mathematics of the nineteenth century is the 



