384 



NATURE 



[November 17, 192 1 



Engineering for October 28. The principal exf>eri- 

 ments described had for their object the determina- 

 tion of the suitability " of the material for steam- 

 turbine blades. In 1916 the British Thomson Co., 

 of Rugby, fitted in one of their turbines an experi- 

 mental wheel having blades of phosphor-bronze, nickel- 

 bronze, brass, mild steel, and stainless steel. Of the 

 four stainless steel blades inserted two were hardened 

 and the other two were hardened and tempered. 

 This turbine was at work from the autumn of 19 16 

 until April, 19 18, when it was opened out for the first 

 time. All the blading was In good condition, but the 

 stainless blades were the only ones entirely free from 

 erosion or corrosion. The machine was put to work 

 again and re-examined last July, when it was found 

 that' the stainless steel blades appeared to be abso- 

 lutely unaffected by their service ; further, the 

 hardened and tempered blades were in as perfect 

 condition as the hardened blades. All the other 

 materials had suffered, some severely. Messrs. Firth 

 and Sons fitted stainless blades 28 in. long into a 

 turbine four or five years ago, and report that these 

 also have given entire satisfaction. Other confirma- 

 tory experiments are described in the article. The 

 subject is of very great importance in turbine manu- 

 facture, and it would appear from the tests that 



in turbine Wading erosion and corrosion trouble can 

 now be entirely eliminated. 



The new catalogue (No. 364) of important and 

 rare books on natural history, issued by Messrs. B. 

 Quaritch, of 11, Grafton Street, W.i, contains nearly 

 800 titles. Interesting items we have noticed are two 

 volumes of the "Index Kewensis " (1885-95), an 

 edition, published in 1836-39, of Cuvier's " Basis of 

 the Natural History of .Animals," a Settin edition of 

 Gilbert's " De Magnete," a copy of the first edition 

 of Darwin's "Origin of Species," and the extensive 

 collection of English and foreign pamphlets on Dia- 

 tomaceae, from the library* of the late Wynne E. 

 Baxter. 



Messrs. Longmans and Co. have in the press a 

 new book by Prof. A. W. Stewart entitled " Some 

 Physico-Chemical Themes," which is intended to 

 form a connecting link between systematic text-books 

 of physical chemistry and the original literature of 

 the subject. Among the subjects treated of will be 

 double and complex salts, pseudo-acids and indicators, 

 non-aqueous ionising media, colloids, the Brownian 

 movement, absorption, catalysis, chemical affinitv, 

 emission spectra, the determination of Avogadro's 

 constant, the periodic law, and atomic structure. 



Our Astronomical Column. 



Bright Assemblage of Morning Stars.— Mr. W. F. 

 Denning writes : " During the remainder of the pre- 

 sent month there will be visible before sunrise all the 

 brightest planets, viz., Mercury, Venus, Mars, 

 Jupiter, and Saturn, and in addition to these objects 

 the crescent of the Moon will be visible in the south- 

 eastern sky from about November 25-28. 



■* It is only at long intervals that so large a number 

 of interesting planets occupy positions in the heavens 

 enabling them to be viewed at the same time. To- 

 wards the end of the month Mars, Jupiter, and 

 Saturn will be near one another, and they will be in 

 conjunction with the Moon on November 25. Mer- 

 cury and Venus will also be near together and low 

 in the south-eastern sky, and on November 28 they 

 may be seen near the narrow crescent of the inoon. 

 The best time at which to view these objects will be 

 from about 6.30 to 7 a.m. Of the planets named 

 Venus will appear to be much the brightest, while 

 Jupiter will rank second." 



Medieval Astronomical Instruments in India. — 

 Memoirs of the Archaeological Survey of India (No. 12) 

 contains a description by G. R. Kaye of some medieval 

 instruments of beautiful workmanship now in the 

 Delhi Museum. There are three astrolabes belonging 

 respectively to the thirteenth, fifteenth, and seven- 

 teenth centuries. They contain planispheres on which 

 the principal stars are delineated with such accuracy 

 that the date of construction can be ascertained within 

 a few years by simple measurement of longitude. 

 The stars' names are recorded in Arabic, and a glos- 

 sary of their meanings is given in the memoir. It 

 may be noted that the name Achernar (the last of 

 the river) is applied to the third magnitude star 

 B Eridani, not to the bright star, 17° further south, 

 that now bears it. . 



There are also tablets on the astrolabes giving the 



NO. 2716, VOL. 108] 



latitudes of several towns, and other details such as 

 the length of the longest day. 



The celestial sphere is of brass 65 cm. in diameter ; 

 it bears the date a.h. 1087 (or a.d. 1676). In spite 

 of the small scale, the stars' positions are so accurate 

 that their measured longitudes led to the date 1664. 



It is of interest to note that the Arabs borrowed at 

 least three constellation names — Thaur, Oantaurus, 

 and Qitus — from the Greek, and that they call Betel- 

 geux and Bellatrix the right and left shoulder of 

 Orion ; in other words, they take the figure as shown 

 on a star-map, not on a globe, as some medieval 

 European astrologers used to do. 



Nova Aquil;e. — It is praiseworthy that of late 

 years a number of observers have studied novae on 

 their decline, long after they have ceased to be 

 spectacular. Comparison of their ultimate with their 

 original condition is of value as likely to afford in- 

 formation as to the character of the event that pro- 

 duced the sudden outburst. Nova Aquilae is a par- 

 ticularlv favourable star to take for this purpose, as 

 a long series of photographs of the star in its pre-nova 

 state is available. It was then of about the loth 

 magnitude, but seemed to be irregularly visible to the 

 extent of half a magnitude. 



Popular Astronomy for October contains, in its 

 Variable Star Report, numerous observations of the 

 star made last summer. Each of the following values 

 is the mean of about eight obser\'ations : — 



1921, June 8, 9-44 mag. ; July i, 9-47 mag. ; July 13, 

 0-64 mag. ; July 28, 9-60 mag. ; August 6, 047 mag. 

 The observations leave it an open question whether 

 there are short-period fluctuations ; if such exist, their 

 amplitude can scarcely exceed 02 mag. It will be 

 seen that the star, in three years from the outburst, 

 has declined to within some half-magnitude of its 

 original brightness. 



