October 8, 19 14] 



NATURE 



151 



brighter, some darker, than the field, and a liquid 

 having the same refractive index as the mineral can 

 be quickly chosen. 



Pr-acticvl methods of determining the critical loads 

 for long struts of var\'ing section have attracted some 

 attention recently. The latest contribution to the 

 subject is given in an article in Engineering for Octo- 

 ber 2 by Messrs. L. Bairstow and E. W. Stedman, 

 of the National Physical Laboratory. The method 

 described seems to be comparatively easy to apply, and 

 has the advantage of being applicable with equal ease 

 to the simplest or to the most general case. It was 

 devised originally for finding the critical loads of 

 wooden struts as used in aeroplane construction. An 

 assumed critical load for the strut is guessed or 

 obtained by an approximate method such as taking 

 Euler's law for a uniform strut of the average sec- 

 tion. Curves for —d'y/dx', dyjdx and v, which 

 comply with the conditions imposed, are then drawn 

 by a process of trial and error described in the article. 

 If the assumed value of the critical load has happened 

 to be correct, the ordinate of the dyjdx curve becomes 

 zero at the middle of the strut (for a strut hinged at 

 both ends). If the assumed value has been incorrect, 

 the ordinate becomes zero at some other point. After 

 two attempts, a very close approximation to the value 

 of the critical load is reached. 



Erratum. — In Nature of September 24, p. 95, col. 

 i., for Dr. S. N. Shannus read Dr. H. S. Stannus. 



OUR ASTRONOMICAL COLUMN. 



A New Comet. — The Times of October 3 publishes 

 I telegram from South Africa announcing the dis- 

 overy of a bright comet by Mr. Lunt at the Royal 



Observatory, Cape Town, on September 18. Mr. 



Wood, of Johannesburg, computed the orbit, and the 



following is the ephemeris given : — 



Right Ascension Declination 



h. m. s. . , 



Oct. I ... 22 48 48 ... —26 44 



5 ... 22 23 36 ... 17 41 



9 ... 22 8 44 ... II II 



13 ... 21 59 24 ... -6 34 



Perihelion passage took place on August 5. While 

 the comet is decreasing its southern declination and 

 reaching a better position for observation in this 

 country its brightness is stated to be fading fairly 

 rapidly owing to the increasing distance from the sun. 

 On October 9 the comet will be situated in the con- 

 stellation of Aquarius, a little below the third magni- 

 tude star gamma. 



The following elements, based by Mr. Wood on 

 observations made on September 21, 24, and 27, have 

 been since communicated by the Royal Astronomical 

 Society : — 



T = 1914 Aug. 499 G.M.T. 



w =270° 19'^ 



0,= o' 22'W9i4-o 



i = It 51'i 

 log ^=9-8543 



Comet 1913/ (Delavan). — Delavan's comet is now 

 badly situated for evening observation, so most should 

 je made of the morning hours. The object is 

 rapidly decreasing its northern declination and moving 

 westward, and will pass perihelion on October 26. It 



NO. 2345, VOL. 94] 



is now situated in the constellation of Canes Venatici, 

 and on October 10 will not be far from the third 

 magnitude star, 12 Canes Venaticorum. The follow- 

 ing eight-day ephemeris is taken from Knowledge for 

 .August last : — 



The Return of Encke's Comet. — The short-period 

 comet known as Encke's comet, for he it was who 

 first calculated its elements, although Pons, of Mar- 

 seilles, actually discovered it in the sky, was due to 

 return this autumn, its period being about three and 

 one-third years. It is now reported {Daily Telegraph, 

 October 2) that it has been observed from the Russian 

 Observatory at Simeis in the Crimea, this information 

 having been received from Prof. Backlund, the director 

 of the Pulkovo Observatory. It is situated in the 

 constellation of Perseus. Encke's comet is of his- 

 torical interest for several reasons. It was only the 

 second instance of the recognised return of a comet, 

 Halley's comet having preceded it by sixty-three years. 

 It was also the first example of a new class of celestial 

 objects revolving round the sun within the orbit of 

 Saturn and exhibiting certain planetary affinities in 

 the manner of their motions. 



Enhanxed Lines and the Presence of Hydrogen. 

 — No. 85 of the Contributions from the Mount Wilson 

 Solar Observatory is devoted to some electric furnace 

 experiments on the emission of enhanced lines in a 

 hydrogen atmosphere. The author, Mr. A. S. King, 

 used in this research the vertical Rowland grating 

 spectrograph described in this column on September 24. 

 The experiments included the production of the en- 

 hanced lines with the furnace in a partial vacuum and 

 in hydrogen at varjing pressures up to one atmo- 

 sphere, and the use of greatly different amounts of 

 titanium. After describing the details of the experi- 

 ments Mr. King sums up his results in three brief but 

 interesting paragraphs. The experiments failed to 

 show any effect of a hydrogen atmosphere in 

 strengthening enhanced lines. The enhanced lines 

 appear in the furnace at low pressures with equal ease 

 whether hydrogen is present or whether the furnace 

 contains a residue of air. No material effect on the 

 relative intensities of enhanced lines is indicated, even 

 when widely differing amounts of titanium vapour at 

 low pressure and at the same temperature are em- 

 ployed. Increasing the pressure of hydrogen, the 

 temperature being held as nearly constant as pos- 

 sible, causes a progressive weakening of the titanium 

 enhanced lines, until at atmospheric pressure only 

 traces of the strongest are visible in the furnace spec- 

 trum, Mr. King finally directs attention to the bear- 

 ing of these results on the study of stellar atmospheres 

 and the value of the strength of enhanced lines as a 

 criterion not only for stellar temperatures but for 

 different regicwis and levels of the solar photosphere. 



The Leeds Astrono.mical Society. — Vol. xxi. of the 

 Leeds Astronomical Society contains the Journal and 

 Transactions for the past year. The volume is edited 

 by Mr. C. T. Whitmell, and gives a good account of 

 the activity of this society. At each of the seven meet- 

 ings which took place a paper on some definite subject 

 j was read, and these are reproduced more or less in 

 I full in this report. Thus some of the contributions 

 i dealt with the spectroscope, Uranus as a view-point, 

 j history of astronomy, etc. Other work of the society 

 } is summed up in the latter part of the volume. 



