July 24, 1919] 



NATURE 



4H 



balloon the temperature of the gas was uniform, 

 although there was a difference of 25° G. between 

 this and the gas temperature at the top. It is cal- 

 culated that in still air as much as 80 per cent, of 

 the total heat loss from the upper surface of the model 

 might be due to radiation from the fabric. For 

 obtaining the minimum heating effect on an airship 

 in sunlight the use of aluminium-coated fabric is 

 recommended, since this also affords good protection 

 against actinic light. 



Ix view of the successful round voyage of the naval 

 ^irship R34, great interest is attached to a fully 

 illustrated account of this vessel which appears in 

 Engineering for July 18. The vessel has a length 

 of 645 ft. over all, and a maximum diameter of 

 78 ft. 9 in. Its gas capacity is about 2,000,000 cub. ft., 

 giving a gross lift of 60 tons under standard condi- 

 tions. The disposable lift is just under 30 tons. The 

 hull is of fine stream-line form, and is constructed 

 of main transverse frames spaced 10 metres apart, 

 and built in the form of a polygon with thirteen sides. 

 The frames are joined at each angle of the polvgon by 

 longitudinal girders, and there are intermediate frames 

 in each space, both transversely and longitudinally. 

 The exterior polygon of twenty-six sides thus formed 

 has the outer cover stretched over it. The girders are 

 constructed of duralumin. Tht>re are eighteen gas- 

 bags, compose J of high quality single-ply cotton 

 fabric, lined with rubber on the inner surface. On 

 this surface goldbeaters' skins are stretched and 

 • rured with rubber solution, and the whole is then 

 nnishi'd over. Each gas-bag has an automatic relief 

 \ live. There are five cars, one for navigational pur- 

 poses, and all the others contain engines. The five 

 engines are of 270 h.p. each, and give a speed of 

 55 knots in still air. The photographic illustrations 

 of the ship under construction and in flight are 

 particularly interesting, and give very clear views of 

 the details of construction. 



Messrs. Hodder and Stol-ghton have in the press 

 the New Teaching .Series, which has been arranged 

 to meet new demands in education as to method and 

 curriculum. The subjects of the volumes in hand 

 include : — Chemistry from the Industrial Viewpoint, 

 Applied Botanv, Industrial Geology, Geography of 

 Commerce and Industry, Chemistry and Bacteriology 

 of .\griculture. Everyday Mathematics, Mathematics { 

 of Engineering, Foundations of Engineering, Mathe- ! 

 matics of Business and Coinmerce, and Industrial I 

 History. 



Messrs. H. K. Lewis .and Co., Ltd., have removed ! 

 their publishing, wholesale, and advertisement depart- 

 ments to 28 Gower Place, W.C.i. The change not 

 onlv provides larger and more convenient accommoda- 

 tion for publishing work, but the .space vacated 

 in the old premises affords much needed additional 

 room for the library and bookselling business. A new 

 and convenient reading-room is to be added to the 

 library over the present library room. 



Messrs. Longm.ans ask us to say, in correction of 

 an announcement in last week's Nature, that though 

 the edition on large paper of " .\ Naturalist's .Sketch 

 Book." by A. Thorburn, which they will publish in 

 the autumn, will be limited to 105 copies, the ordinary 

 edition of the book will not be limited in number. 



The offices of the Imperial Mineral Resources 

 Bureau have been moved from 14 Great Smith Street 

 to 2 Queen .Anne's Gate Buildings, Westminster, 



AV.i 



. NO. 2595, VOL. 103] 



OUR ASTRONOMICAL COLUMN. 

 A Bright Meteor.— .\ large meteor with unusually 

 slow motion was observed at Bristol on July 20, 

 II. 2 G.M.T. ; it had a double nucleus, and passed 

 over 42° of the sky in 12 seconds. The observed path 

 was from 37°+47° to 4°+i5i°. The meteor was of 

 a red colour, like Mars, and probably from a radiant 

 in Leo at about 155° + 25°. It is curious that the 

 great fireball seen in America on July 20, i860, had a 

 radiant point in the same region of the sky, and mav 

 be assumed to have been derived from the same 

 cometary .system. Further observations of the meteor 

 of July 20" last would be valuable, and Mr. W. F. 

 Denning, 44 Egerton Road, Bristol, will be glad to 

 receive any. 



The Light of the Aurora and the Auroral Line, 

 —Observation of the brightness of the background of 

 the sky by various observers has shown that it must 

 be due to some other cause than the diffused light of 

 the stars themselves, and the suggestion has been 

 made that this is the effect of the existence of a per- 

 manent aurora. In the Astrophysical Journal for May 

 Prof. Slipher publishes an account of some spectro- 

 graphic observations which have a direct bearing on 

 the point. He says that during three and a half vears 

 something like one hundred spectrograms were made 

 of the night sky, and every one of them recorded the 

 chief auroral line, so that during this period of time 

 auroral illumination of the skv was found to be present 

 on every night that an exposure was made for detect- 

 ing it. Incidentally, Prof. Slipher made a determina- 

 tion of the wave-length of the green auroral line, 

 which he finds to be longer than the generally accepted 

 value, A5571. Prof. Frost, in an editorial note, cor- 

 roborates the fact froin inspection of one of the 

 spectrograms that the green line falls at a point of 

 greater wave-length than the solar line A 5573, and it 

 appears that the wave-length of the auroral line is 

 substantially A 557805. 



The Spiral Nebul.*;.— A reprint from tlx^ Journal 

 of the Washington .Academy of Sciences for April 19 

 gives an abstract of a lecture delivered by Prof. H. D. 

 Curtis, of the Lick Observatory, on certain modern 

 theories of the spiral nebulae. The author forms the 

 opinion that these nebulat; are island universes, and 

 not part of our galactic system, a line of argument 

 adduced to show this being as follows :^The spiral 

 nebulae have large radial velocities shown by the 

 spectroscope, their average speed being nearly five 

 hundred miles a second, but by repeating photographs 

 taken about thirteen years ago and comparing them 

 with the earlier ones. Prof. Curtis finds no evidence 

 of proper motion or motion at right angles to the 

 line of .sight which it is to be expected these objects 

 should have, since their .space velocity is high. The 

 conclusion to be drawn is that the cross-motion does 

 not show because the nebulae are very remote, so 

 remote that they must be far outside the generally 

 accepted limits of the bun-shaped figure known as 

 our stellar system. An argument in favour of the 

 island universe theory, drawn from the appearance of 

 Novae, may be repeated. The brighter Novae of the 

 past have almost invariably been located in or close 

 to our Milky Wa\-. and therefore have evidently been 

 part of our stellar system. In the course of a few 

 years a dozen Novae have been found in spiral nebulae, 

 all very faint, and the life-history of these has been 

 essentially the same as that of the brighter Novse. 

 There is thus a presumption, though not a very rigid 

 proof, that the phenomena of the spirals are similar 

 to those of our galaxy, and therefore that they th<^m. 

 selves are galaxies. 



