206 



KNOWLEDGE. 



[September 1, 1894. 



It will be remembered that in the enlargements from the 

 Henry photographs similar nebulous ligatures between 

 stars were observable, joining them up into branching 

 streams radiating outwards from the central regions of 

 the cluster. We therefore appear to have corroborative 

 evidence in these photographs by Mr. Wilson, proving 

 that in both the inner and outer parts of the cluster the 

 stars are physically connected with one another in streams 

 which seem to be radially arranged with respect to the 

 centre of the cluster, and that these streams of stars 

 linked together by nebulosity are intimately associated with 

 streams or patches of the light-absorbing material which 

 gives rise to the dark lanes or patches. 



PHOTOGRAPHS OF RORDAME'S COMET. 



The photograph of Kordame's comet, published in the 

 •July number of Knowledge, is referred to as having been 

 sent to me by Mr. ,J. N. Cobb, of Philadelphia, who 

 obtained it from Mr. Alfred Rordame, of Salt Lake City, 

 Utah. I have since learned, by letters received from Mr. 

 Eordame as well as from Mr. Cobb, that the photograph 

 was taken by Prof. W. J. Hussey, when on a visit to 

 Mount Hamilton, with the Crocker telesco^^e of the Lick 

 Observatory. Prof. Hussey has also kindly sent me glass 

 transparencies of five other photographs of Rordame's 

 comet, making in all six photographs, obtained by Prof. 

 Hussey on the 12th, 13th, 14th, loth, 16th and 18th of July, 

 1893. I have reproduced three of the glass transparencies 

 on the accompanying plate. The photograph taken on the 

 13th was reproduced in the July number, and those taken 

 on the 1.5th and IGth have arrived in a scratched condition, 

 which makes them unsuitable for reproduction, but they 

 form a most interesting series, illustrating the great 

 rapidity with which the tails of small comets vary in form 

 from day to day. For the purposes of reproduction silver 

 prints or platinotypes from the original negatives are 

 generally preferable to copies on glass, which are very apt 

 to get injured. The streamers of the tail appear to issue 

 from the centre of the nucleus, and not from either side of 

 the envelopes about the comet's head, as the drawings of 

 some of the larger comets would lead one to suppose, but 

 this may possibly be due to photographic irradiation, which 

 causes the bright nucleus and surrounding envelopes of 

 the comet's head to appear on the photographs larger than 

 they really are. 



Notices of Boofes. 



Celestial Objects for Common Telescopes. Vol. II. Fifth 

 Edition ; revised and greatly enlarged by the Rev. T. E. 

 Espin, M.A., F.R.A.S. (Longmans, Green & Co., 1894.) 

 The re-editing and bringing up to date of this valuable 

 book must have been a very diiEoult task, but Mr. Espin 

 has accomplished it with great tact and discretion, leaving 

 sufficient of the original matter unaltered to preserve the 

 charm of Prebendary Webb's style, and yet adding suffi- 

 ciently to the text and in foot-notes to bring the work 

 abreast with the time. The earlier editions of " Celestial 

 Objects " appeared when comparatively little had been 

 done in stellar spectroscopy, and Mr. Webb had modestly 

 decided not to attempt to enter upon the subject, as being 

 too difficult for himself and his readers ; but this subject 

 has now become such an important department of modern 

 astronomy, and so many more amateurs now make use of 

 spectroscopes, that spectroscopy could no longer be ignored. 

 Few better men than Mr. Espin could have been found to 

 bring up to date the stellar chapters of Mr. Webb's 

 classical handbook, and he has evidently worked at it as 



a labour of love. The second volume, which now appears, 

 contains only the chapters referring to stars, clusters and 

 nebulte. The division of the book into two volumes is 

 necessitated by its increased bulk due to the growth of 

 observational astronomy, and the division is convenient, 

 for this portion of the book is the part which will be 

 most required for use in the observatory, while the first 

 volume may be kept for indoor use. The descriptions of 

 celestial objects are now arranged in order of their right 

 ascension in each constellation, thereby saving the fifty 

 pages of Appendix II. in the fourth edition. 



A Treatise on Astronomical Spectroscopy, being a translation 

 of "Die Spectralanalyse der Gestirne." By Prof. Dr. J. 

 Scheiner. Translated, revised, and enlarged by Edwin 

 Brant Frost, M.A., Assistant Professor of Astronomy in 

 Dartmouth College. (Ginn & Co., Boston and London, 

 1894.) The thanks of astronomers are due to Prof. Frost 

 for the labour he has bestowed upon this English edition 

 of Prof. Scheiner's book. In many parts of the work he 

 very closely follows Prof. Scheiner, but in others he has 

 needed to expand the text considerably in bringing the 

 work up to date. An interesting fact, indicating the 

 relative compactness of the English and German languages, 

 may be noted, where Prof. Frost has most closely followed 

 Scheiner's original ; the English saves one page in about 

 every ten of the German. The book will be welcomed by 

 all English-reading spectroscopic observers. 



The following books have been received for notice : — 



Practical Work in General Physics. By W. G. Wooll- 

 combe, M.A., B.Sc. (Clarendon Press.) 



Fifth Annual Beport of the Missouri Botanical Garden. 

 (St. Louis, Mo.) 



The Stereoscope and Stereoscopic Photor/raphy. From the 

 French of F. Drouin. (Percy Lund & Co.) 



H 1 1 1 f r s . 



[The Editor does not hold himself responsible for the opinions or 

 statements of correspondents.] 



A PROLONGED SUNSPOT MINIMUM. 

 To tlie Editor of Knowledge. 



Dear Sib, — The partial suspension of solar activity, 

 estabUshed by Mr. Maunder in his article entitled as above 

 (Knowledge, August, 1894), represents a curious phase of 

 solar history. There is, besides, strong, although indirect 

 evidence that the "prolonged sunspot minimum" was 

 attended by a profound magnetic calm. This evidence is to 

 be found in the auroral records of the time. For the con- 

 nection between the occurrence of aurora? and the magnetic 

 condition of the earth is so close, that the absence of one 

 kind of disturbance may safely be held to betoken the 

 absence of the other. 



Now in England, during the whole of the seventeenth 

 century, not an auroral glimmer was chronicled. Stowe 

 recounts that on the 14th and 15th of November, 1574, 

 " the heavens from all parts did seem to burn marvellous 

 ragingly"; * and the next similar occurrence took place on 

 March 17th, 1716. Upon his observations of this fine 

 display, Halley founded his magnetic theory of aurorse.f 

 The event created an extraordinary sensation throughout 

 the country, some slight and partial sky-illuminations in 

 1706 and 1709 having escaped general notice. 



* Annates of England, p. 678. 



t Philo-iopliical Transactions, Vol. XXIX., p. 407. See also E. J. 

 Lowe's " Chronology of the Seasons," quoted by Dr. Garnett in 

 Mature, Vol. III., p 46. For a fuller account of auroral history 

 during this period we may refer to the Mdinhurgh Eeview, No. 336 

 (October, !886;, pp. 418-421. 



