232 



NATURE 



[November 22, 19 17 



ing for November 2, 9, and 16, will ibe read with in- 

 terest, as i't forms a valuable contribution to our know- 

 ledge of this subject. Mr. Webb has evolved a graphical 

 method of sol utio n for non-cylindrical shafts, in which 

 a graph of VI/w is drawn for the shaft, w being the 

 weight per unit length, and I the moment of inertia of 

 the section in bending. The whirling speed can then 

 be estimated roughly from a set of typical curves 

 included in the paper, or can be calculated by employ- 

 ing graphically Mr. Webb's two fornlulae. For the 

 purpose of checking the new method, a namber of 

 new solutions has been found by rigorous mathematics. 

 These cases include a cylindrical shaft, a solid shaft 

 consisting of one or more conical pieces, a hollow shaft 

 with all its weight in the rim, and consisting of one 

 or more conical pieces, and a solid shaft the meridian 

 curve of which consists of one or more parabolic arcs, 

 all of them, produced if necessary, touching the axis. 

 For all cases the agreement is remarkably close, 

 and shows that the new graphical method is valid if 

 (maximum value of I'«')/(minimum value of \w) is 

 less than 40,000, which limit probably includes all 

 shafts likely to be required in practice. Mr. Webb's 

 method is based on a hitherto unpublished approxi- 

 mate method of attacking the general problem devised 

 by Mr. W. H. Barling some years ago. Mr. Barling's 

 hypothesis is that there is no transference of energy 

 between consecutive elements of the shaft, and it gives 

 correct results for cylindrical shafts. 



Messrs. J. M. Dent and Sons, Ltd., will shortly 

 publish "A Complete System of Nursing," by Miss 

 A. M. Ashdown. It is claimed for the work that it 

 will contain all the practical information which a 

 nurse may require during her training and in actual 

 practice. 



Messrs. Dulau and Co., Ltd., 37 Soho Square, 

 W.I, have just issued a valuable and interesting cata- 

 logue (No. 6q, November) of more than 1600 works 

 on Botany (Phanerogams and Cryptogams), Zoology 

 (Vertebrates and Invertebrates), Herbals, Gardening, 

 and Agriculture. Many of the books offered for sale 

 are rare, and a considerable proportion, being of 

 foreign origin, are difficult to obtain in a new condi- 

 tion at present. The catalogue should be of service 

 to many of our readers. 



In the article on " Ferro-Concrete Ships" which ap- 

 peared in last week's Nature, it should have been 

 stated that we were indebted to Engineering for the 

 blocks with which the article was illustrated. 



OUR ASTRONOMICAL COLUMN. 



Orbits of Comets. — The orbits of three comets are 

 discussed by S. Ogura in Annales de I'Observatoire 

 Astrononiique de Tokyo, tome v., part 3. (i) Comet 

 1827 II. was discovered by Pons on June 20, 1827, 

 and observed by him for a month ; Pons used a ring 

 micrometer, and his observations show rather large 

 residuals. The definitive orbit is as follows : — 

 T = 1827 June ;-i92422 G.M.T. 

 (o — 19° 18' s6-i2"'j 

 ^=317^ 39' 39-67" r 1 827-0 

 z = 136° 26' iroo'j 

 log ^ =9-9067087 

 log <? =9-9774915 

 Period = 63-83 years 



The period is considered to lie between fifty-nine and 

 sixty-nine years. The orbit of the comet of 1500 shows 

 a distant reseijiblance, but identity is improbable. 



(2) The comet of 1132 was observed in Japan on 

 October 5, 7, and 9; its motion was extremely rapid, 



NO. 2508, VOL. 100] 



100° being described in four days. The following 

 orbit is deduced : — 



T = ii32 August 30-20 G.M.T. 



ft) =114-3 I 



^ = 201-1" [i 132-0 



/ = 1 06 4' J 

 log ^ =98666 

 These elehients indicate a near approach to the 

 earth, the distance being 0045 on October 7. This 

 comet was also observed in China and Europe, but 

 the positions are less precisely defined than in the 

 Japanese record. 



(3) The comet of 1240 was observed with consider- 

 able precision in Japan ; it passed close to Jupiter, 

 and the head was stated to be "as big as Venus." 

 The following orbit is deduced from the Japanese and 

 Chinese observations : — 



T = 1240 January 21-06 G.M.T. 



« ==331-3" I 



^ = 124-5- -1240-0 



log^ =98246 

 The minimum distance from the earth was 0-36 on 

 February 2. The orbit somewhat resembles that of 

 comet 1863 IV. 



The Iron Arc as a Source of Standard Wave- 

 lengths. — Previous investigations have shown that the 

 wave-lengths of many of the lines in the spectrum of 

 the iron arc, which is in such frequent use as a source 

 of standard wave-lengths, are subject to variations 

 depending upon proximity to the electrodes. The pos- 

 sible elimination of this "pole-effect" has been the 

 subject of an important investigation by Messrs. St. 

 John and Babcock (Astrophysical Journal, vol. xlvi., 

 p. 138). It has been shown that the effect disappears 

 in the case of the Pfund arc in vacuo, and becomes 

 negligible in a narrow central zone of the same type 

 of arc in air when the negative pole is of carbon. 

 The former, however, is not a convenient everyday 

 source, and the latter is lacking in intensity. The 

 practical outcome of the extensive experiments is to 

 show that a Pfund arc, with both poles of iron, may be 

 relied upon to give the " fundamental " wave-lengths of 

 even the most sensitive lines, if the length of the arc 

 be not less than 8 mm. and the current not more 

 than 5 amperes ; under these conditions a horizontal 

 zone near the centre at least ij mm. wide may be used 

 with safety. This arc also has the advantage of giving 

 sharply defined lines, and uniformity in the relative 

 intensities. The investigation has shown that the pole 

 effect has not been entirely eliminated in the case of 

 the adopted international standards, and that certain 

 supposed anomalous displacements of iron lines in the 

 sun become normal when the fundamental wave- 

 lengths of such lines are used for comparison. 



Cape Observatory Report. — The report of his 

 Majesty's Astronomer at the Cape of Good Hope for 

 1916 has been received. Besides work of a more or 

 less routine character, we note that a new programme 

 of observations of close circumpolar stars with the 

 reversible transit-circle has been undertaken, with 

 special reference to the determination of the constant 

 of aberration. Mr. J. Voute has completed his series 

 of observations for stellar parallaxes by means of right 

 ascension measures, and has also made observations 

 of double stars. The programme of observations for 

 radial velocities of stars with the Victoria telescope and 

 four-prism spectrograph was completed before the end 

 of the year, and experiments with a shorter camera 

 are in progress with a view to the extension of the 

 observations to fainter stars. Photographs of the sun, 

 intended to supplement the Greenwich series, were 



