Sept. 25, 1884] 



NA TURE 



5ii 



girders. There is a very clear analysis of the strains on 

 the struts and ties in the lattice girder ; the construction 

 and sectional area of each strut and tie is worked out : 

 next the suspension bridge is discussed, the general con- 

 struction being explained. 



The last few subjects treated in the volume include 

 the fire-engine and gas-engine, with several other short 

 accounts of the newest inventions, concluding with a 

 chapter on the strength of materials. 



In the publishers' preface we read that the present work 

 is intended to furnish a reliable guide to practical engineers 

 and others connected with the engine-shop and building- 

 yard. This end has been most satisfactorily accom- 

 plished, and both authors and publishers may be con 

 gratulated on having placed before the public a most 

 useful book ; the printing is exceedingly clear, and the 

 illustrations in the text good ; the separate series of 

 engraved plates add much to the value of the volume, 

 without which many long descriptions would have been 

 necessary. The book deserves a place in every technical 

 library in the country. Those learning any branch of 

 mechanical engineering will do well to study it, for it is 

 one of the few really practical works published. 



OUR BOOK SHELF 



Catalogue and Handbook of the Archaeological Collections 

 in the Indian Museum. Part II. Bv John Anderson. 

 (Calcutta.) 

 We have already drawn attention to the first part of this 

 excellent Catalogue, which thoroughly fulfils its promise 

 of being not only an exhaustive list of the valuable ob- 

 jects in the Indian Museum, but a scholarly guide to them 

 as well. The second part is occupied with Buddhist, 

 Jain, Brahminical, and Mohammedan sculptures, and with 

 the collections from Southern India, Persia, and other 

 parts of the East. Appendixes have been added at the 

 end of the book, including two by Prof. Warden and Mr. 

 Growse. The work will be of great value to students of 

 Indian archaeology, and more especially to those who are 

 devoting themselves to Buddhistic research. The Indian 

 Museum is naturally a storehouse of antiquities throwing 

 light on the past history of India and its relations with 

 the West, and these have now been brought to the know- 

 ledge of scholars in a thoroughly satisfactory way. 



LETTERS TO THE EDITOR 



[ The Editor does not hold himself responsible for opinions expressed 

 by his correspondents. Neither can he undertake to return, 

 or to correspond with the writers of, rejected manuscripts. 

 No notice is taken of anonymous communications. 



[ The Editor urgently requests correspondents to keep their letters 

 as short as possible. The pressure on his space is so great 

 that it is impossible otherwise to insure the appearance even 

 of communications containing interesting and novel facts .] 



Barnard's Comet 



Last night (September 22) this comet was well seen in the 

 3-foot telescope. It was large (at least 4' over), brighter to the 

 middle, but without nucleus ; a position was measured from a 

 faint star involved in the light of the head. At Sh. 20m. the 

 position by circle reading was a ic,h. 45m. 50s., and 117 16' 30" 

 N.P.D. A. A. Common 



Ealing, September 23 



The Krakatoa Eruption 

 By this morning's post I have received, in a rather round- 

 about way from India, a translation of a Dutch account of the 

 Krakatoa eruption, which, if you have not had it already, seems 



to contain some interesting variations on, or additions to, the 

 mass of matter that you have already printed on that subject. 

 Indeed the only postscript that could now be well added to it is 

 the comfortable and encouraging discovery of the late French 

 scientific expedition to the effect that the eruption is now posi- 

 tively over. The Batavians, as you are probably aware, feared 

 that another eruption was preparing, in consequence of the im- 

 mense number of stones still being ejected and clouds of smoke 

 emitted. But the French savants discovered that no stones 

 were being thrown up, only immense quantities of them tumbling 

 down the mountain's sides ; and this because the material, of 

 which those new sides of the mountain are now composed, 

 is so extraordinarily friable that the heat of the sun each day 

 bleaks them up, and the quiet force of gravitation brings the 

 pieces galloping down the steep slopes, and plunging at last into 

 the danger of passing vessels, — but only by day. and 

 when th-: sim is shining, for at night everything is quiet ; and 

 if by day and night a cloud forms above the mountain-top, it is 

 neither smoke nor gaseous emanation, but merely the infinitely 

 fine powdery matter of the broken-up and rolling stones of the 

 day rising into the air and moving along with its currents up 

 along the slopes which have been warmed by the sun. 



C. Piazzi-Smyth 

 15, Royal Terrace, Edinburgh, September 15 



The Sky-Glows 



I was not aware before reading Mr. Leslie's letter in 

 Nature of the nth inst. (p. 463) that any of the phenomena 

 supposed to be connected with the volcanic dust had been seen 

 before the eruption of Krakatoa in May iSSj. Would the 

 whole text of the description of those seen in February 1S83 in 

 Natal, from which Mr. Leslie gives a quotation, indicate them 

 to be exactly similar to those seen since the great eruption ? 

 Where can a description of them be found ? 



The remarkable suusets reported as seen in Mauritius after 

 May 1SS3 and before the great eruption of Krakatoa, were by 

 some attributed to the earlier volcanic disturbance, while 1 ithers 

 have expressed doubts whether they were really similar to those 

 so generally noticed last autumn and winter. 



It was not in the least the purpose of my former letter to 

 imply the necessity of visiting a mountainous country to see the 

 red corona round the sun; I am aware it is still plainly visible 

 in England, and do not doubt even in London in fairly clear 

 weather, having observed it when there in May last, not only with- 

 in an hour of sunset or sunrise, but at all times of the day. But I 

 wished to draw your readers' attention to the fact that this 

 corona is much better seen in the clearer air at great altitudes, 

 where also it is not necessary, as in England, that the sun be 

 hidden by a cloud for it to be well seen. 



I had not seen it stated before that the phenomena have been 

 visible in England for years past. There is much more to be 

 seen than a "blanching of the sun," as Mr. Leslie calls it, so 

 that perhaps we are not both discussing the same phenomenon. 

 Besides the bluish or greenish light immediately round the sun, 

 which is not very striking, there is a broad red or brown band 

 beyond, which is so. Has this been seen in England previous 

 to last November ? It has been habitual for me to scan the 

 neighbourhood of the sun for halos during twenty-five years, 

 and I never observed it previously to the date mentioned. It is 

 true that the circumstances favourable for producing halos are 

 unfavourable for seeing the red ring ; nevertheless, since the 

 latter first appeared in November I have not unfrequently seen 

 it at the same time with a halo. It is also true that I saw por- 

 tions of this red ring some days before I recognised them as a 

 new phenomenon, but then they were only visible in gaps 

 between clouds, so that I took them to be on thin cloud, and 

 simply examples of the nacreous hues of thin films ; any large 

 extent of sky would probably have enabled me to perceive 

 their true character. It is therefore very difficult for me to 

 believe that the corona was visible in this country much, if at 

 all, before last November. 



Whether the phenomenon is ordinarily noticeable in volcanic 

 countries I have not learnt ; information from observers in such 

 places would be of much value towards the elucidation of this 

 interesting question. I gather from Prof. G. II. Stone's state- 

 ment (Nature, vol. xxix. p. 404) that a somewhat similar 

 appearance is commonly visible in Colorado, where it may per- 

 haps be attributed to the higher layers of dust of that very dusty 

 region. T. W. Backhoi i 



Sunderland, September 20 



