86 



KNOWLEDGE. 



[April 2, 1894. 



Notw g of B oolig. 



Celestial Objects for Common Telescopes. By the Rev. 

 T. W. Webb. Fifth Edition, revised and greatly enlarged, 

 by the Eev. T. E. Espin. Vol. I. (Longmans, Green & 

 Co.) This is a new edition of a book which has probably 

 made more astronomical observers than any other book 

 that has been published. It is fourteen years since the 

 fourth edition appeared, and nine years since IMr. Webb's 

 much-lamented death ; and considering the rapid advances 

 which have been made in every brancTa of observational 

 astronomy during the past decade, a new and enlarged 

 edition of the Celestial Objects was much needed. The 

 astronomical public owe a debt of gratitude to Mr. Espin 

 for the trouble and care he has spent upon its production. 

 The bulk of the book has been considerably increased. 

 It will now be issued in two volumes, only the first of 

 which has as yet appeared. The first volume contains an 

 appreciative little memoir of Mr. Webb by his friend and 

 executor Mr. Espin, which is followed by Mr. Webb's 

 chapter on the use of the telescope, to which notes on 

 celestial photography and the use of the spectroscope have 

 been added ; and the old chapters by Mr. Webb on the 

 sun, the moon, the planets, comets and meteors, to which 

 more or less extensive notes have been added by Miss 

 Brown, Mr. Elger, Mr. Stanley Williams, Mr. Waugh, 

 Mr. Freeman, and, last but not least, Mr. Denning. The 

 second volume refers to double stars, clusters, and nebulre, 

 and to its enlargement and bringing up to date Mr. Espin 

 has especially given his attention, greatly adding to its 

 value by his additions. 



The Theory of Heat. By Thomas Preston, M.A. 

 (Dublin). (Macmillan & Co., 189-1 )— This is a com- 

 panion volume to Professor Preston's admirable book, 

 " The Theory of Light," published four years ago. It is 

 a still larger volume, extending to over 700 pages, and 

 embraces a wider range of subjects, which Professor 

 Preston endeavours to deal with historically as well as 

 theoretically. No scientific inquiry is more full of human 

 interest than the study of the nature of heat, for no branch 

 of science is, as Professor Preston remarks, so intimately 

 connected with the every-day occupations of life. Pro- 

 fessor Preston is a lucid exponent of the theoretical parts 

 of his subject, and an interesting writer, who gives a living 

 interest to every subject he touches. All the chapters are 

 methodically arranged and broken into convenient para- 

 graphs. He gives, wherever possible, the classical 

 experiments which have led to the discovery of new facts 

 and important advances in theory, and leads the reader to 

 take a personal interest in the work of Lavoisier, Rumford, 

 Pictet, Herschel, Dalton, Davj', and C4ay-Lussac. His 

 chapters on the early theories of Heat, on Matter, and on 

 Energy, with which the book commences, are particularly 

 to be recommended. 



Life and Bock : a Collection of Zooloyical ami (renlogical 

 Kssai/s. By E. Lydekker, B.A. (Cantab.), F.G.S., F.'Z.S. 

 London : The Universal Press, 326, High Holborn. 1894. 

 • — Onr readers will be glad to see this collection of essays, 

 many of which they will remember in the pages of 

 Knowledge, though they are now in a slightly altered 

 form, having been carefully revised, and in some cases 

 further illustrated by the author. Mr. Lydekker's articles 

 ai-e always interesting and instructive ; probably no other 

 palfGontological writer deals with the problems of evolution 

 and development in so attractive a manner ; he has the gift 

 of putting before his readers multifarious facts and details 

 about dry bones in a way that makes them see the living 

 animal, and follow with interest the logical conclusions 

 to which he deskes to lead them. 



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

 statements of correspondents.] 



A BLACK AURORA. 

 To the Editor of Knowledge. 



Sir, — The appearance of the great sunspot which was 

 visible from February 20th till the beginning of March 

 lends interest to a curious meteor seen by me on January 

 2.5th last, about 8 p.m., at Croydon. It consisted of five 

 dark rays or streamers, which emanated from a point over 

 the northern horizon at or near the true north, and 

 radiated like the spokes of a wheel towards the zenith, or 

 it might be the magnetic zenith. The rays were clearly 

 defined against a hazy sky, which was faintly illuminated 

 by the glare of the metropolis, and resembled five blades 

 of a black outstretched fan. As I looked, the whole 

 system wheeled slowly through an arc of 30^ oi' 40° 

 towards the east, and then faded out. The rays did not 

 seem to quiver or change colour, but remained black or 

 smoky, and reminded me of streaks made by a hair pencil 

 dipped in Chinese ink. I regard the phenomenon as a 

 black aurora, because of its behaviour and the collateral 

 phenomena. Black or smoky pillars and patches have 

 been observed in auroras, but although I have examined 

 the records of hundreds of displays, 1 have seen no account 

 of a similar effect. 



I may add that on the evening of February 28th, about 

 8 P.M., an aurora was seen in Croydon by me and many 

 others. Two white luminous patches, one waxing while 

 the other waned, appeared in the clouded sky near the 

 Great Bear, and several more near the constellation 

 Orion. A dirty greenish arch of difl'ased light over a dark 

 segment also showed above the northern horizon, and 

 gradually spread up the sky nearer to the zenith. The 

 display lasted an hour or more, and was also seen with 

 better eft'ect in other parts of the country, where red 

 streamers emanated from the greenish arch. As the 

 black aurora seems to have heralded the sunspot, and the 

 green display to have followed it, perhaps you will con- 

 sider these observations of some interest. 



Croydon. Yours, J. Munro. 



[If we suppose with Mr. Munro that the dark rays 

 radiating "from a point over the northern horizon" were 

 sufficiently opaque to cut out the light reflected by the 

 atmosphere from the gas lamps of London, we must assume 

 that they were foggy semi-opaque regions in the lower 

 atmosphere, an assumption which entails a considerable 

 strain on the imagination, especially when we remember 

 that the haze-producing particles which reflect the glare 

 from a town probably float at no great height above the 

 ground. 



It seems to me easier to assume that the dark rays were 

 narrow interspaces between broad bright rays. Readers 

 of Mr. Munro's book, " The Romance of Electricity," will 

 congratulate him upon his good fortune in witnessing so 

 curious and interesting a phenomenon. — A. C. Ranyard.] 



To the Editor of Knowledge. 



Beechfield, Heswall, Cheshire, 



19th March, 1894. 

 Dear Sir, — On the 15th of March last, from 6.30 to 7 

 p.m., I observed what, to me at all events, was an unusual 

 appearance, as the sun rose over the lunar crater Clavius. 

 The ridges of the two principal inner craters, being 

 illuminated, showed a brilliant red colour in very marked 

 contrast to the general surface of the moon. The colour 



