4o6 



KNOWLEDGE & SCIENTIFIC NEWS. 



[Apkil, igo6. 



Turkestan, a trans-Caspian area penetrated by the Imperial 

 railwa3's of Russia, and, for travejlers from the West, can be 

 readily reached by way of Naples, Constantinople, Black 

 Sea, Tiflis, Caspian Sea, Bokhara and Samarkand, or the 

 alternative route via Berlin, Warsaw, Moscow, Samara, 

 Orenburij, and Tashkent. On this railway about two- 

 thirds the way from 'I'ashkent to Samarkand lies Jizak, 

 which is only a few miles to the south of the ecli])se central 

 line. Other easily accessible stations near Jizak, are 



Zaamin, Nau, and Ura-tiube, all well within the belt of 

 totality. 



In order to indicate the exact circumstances of the eclipse 

 throughout the length of its track, the local particulars have 

 been calculated for the eleven stations shown .above, and an 

 e.xtra possible station between Yarkand and Cherchen in- 

 cluded from the British Nautical Almanac. 



Stars Having Pec\iliar Spectra. 



.'\ further li.-,t of stars showing special features in their 

 spectra have been detected by Sirs. Fleming during her 

 examination of the Henry Draper Memorial photographs of 

 stellar spectra obtained with the prismatic cameras. 

 R. Cygni. — A photograph of this variable star, taken with 

 the 8-inch Draper telescope on November 19, 1890, shows the 

 spectrum of this star to be class Md (Harvard Notation), 

 having the hydrogen lines H7 and H5 bright. On a later 

 photograph obtained with the same instrument on Decem- 

 ber 7, 1904, the spectrum of this star appears to be of the 

 fourth ty[ic, resembling class Na, and shows no trace of 

 bright hydrogen lines. 



D.M. + 21" i5og. — R.A. = yh. 23.3m.; Decl. + 21° 7' 

 (190°). — This object is in N.G.C. 2392, or identical with it. 

 N.G.C. 2392 was found to have a continuous spectrum, with 

 three bright lines, by Winlock and Peirce, on January 7, 

 1869, and was later found to be gaseous by d 'Arrest. Photo- 

 graphs obtained with the 8-inch Draper telescope on Novem- 

 ber 21, 1900, and November 27, 1905, show no trace of the 

 bright lines characteristic of gaseous nebula;, but that the 

 spectrum is of the fourth type. The images of the object 

 on chart plates, however, are hazy, and the image on a 

 photograph obtained with the Bruce telescope on April 16, 

 1904, shows distinct nebulosity, especially on the preceding 

 and southern edges. 



D.M. -|- 36° 3907. — K.A. = 2oh. 5.8m. ; Decl.= + 360 ^i' 

 (1900) magnitude = 5.5. The spectrum of this star in 

 Cygnus was obtained on plates taken with the ii-inch 

 Draper telescope on July 4 and November 4, 1905, and shows 

 the hydrogen line H S as a fine bright line centrally super- 

 posed un the dark line Hi. 



Device for Developing Corona Photographs 



One of the great dilVnullies encountered in ijhotographing 

 the solar corona during total solar eclipses is caused by the 

 very great range in intensity of the object; in most cases it 

 is necessary to e.\po«- many different plates for carefully 

 arranged times of graduated duration, so that we may ob- 

 tain records of all parts, from the intense inner corona to 

 the delicate tracery of the outer streamers. If a photograph 

 exposed for any considerable time is developed normally the 

 inner corona is generally so dense by the time the outer 

 details are brought out that it is unprintable. 



Numerous suggestions have been brought forward for 



getting over this difficulty, the most successful hitherto 

 being that of Burckhalter, who arranged a car lly calcu- 

 lated series of rotating screens over his photographic plates 

 during expostirc, so that the outer regions received more 

 than the inner parts. These were partly successful in that 

 all parts of the corona could be obtained of printing density 

 on the same negative, but the artificial lines produced by 

 the occulting screens were objectionable. Recently a 

 method has been proposed by Mr. T. Thorpe, which ap- 

 pears to give promise of success. Instead of developing 

 the negative in the ordinary way, it may be mounted on 

 a turntable, and centred so that the centre of the corona is 

 coincident with the axis of rotation. Then by means of a 

 small funnel or pipette mounted on a radial arm also work- 

 ing on the same centre as the plate, begin the development 

 by allowing the developer to fall near the edges of the plate ; 

 afterwards gradually approach the stream of developer from 

 the funnel towards the centre, restraining the developer also 

 if found necessary, as it approaches the over-exposed parts 

 of the inner corona. The centrifugal action due to the 

 rotation of the photographic plate will, of course, prevent 

 any of the developer getting nearer the centre than is de- 

 sired. 



BOTANICAL. 



By G. Massee. 



The Periodicity of Sexual Cells in 

 Dictyota Dichotoma. 



DicTYorA is one of the red seaweeds not tmcommon on our 

 shores. In common with other members of the group, three 

 kinds of plants possessing different functions concerned with 

 reproduction are present. One set of plants produce 

 antherozciids, or male fertilising bodies ; a second batch pro- 

 duce oogonia, or female organs of reproduction ; while a 

 third lot of planis produce tetraspores, or asexual reproduc- 

 tive bodies. The antherozoids, which are motile or possessed 

 of spontaneous movement, and the oogonia are respectively 

 liberated at maturity into the water, when the antheroids 

 approach and fertilise the oogonia. Professor Lloyd 

 \Villiams describes in The Annah of Botany the important 

 discovery that this liberation of the sexual organs is 

 periodic. Several crops succeed each other during the 

 summer months, and each crop from the period of its 

 initiation, maturition, and discharge, occupies a fortnight. 

 This periodicity is found to synchronise with the spring 

 tides, and is expressed by the author as follows : — " So 

 intimate is the relation between the tides and the crops of 

 special cells, that a study of the tidal almanac for any 

 locality will enable us to predict the actual days during- 

 .August and September in any given year on which general 

 liberation and fertilisation of gametes will occur, and even 

 should exceptional conditions prevail, the resulting error 

 will only be about a day earlier or later than the one pre- 

 dicted." 



Several factors are more or less concerned in promoting 

 this periodicity, .among which are variations in the degree of 

 aeration and of pressure; also differences of temperature 

 and illumination ; but the most important stimulus which 

 favours the fortnightly development and liberation of a crop 

 of anthcridia and oogonia is the periodic change in the 

 amount of light, as a direct result of the alternation of neap 

 and spring tides. 



Plants collected in October and kept growing for several 

 nuinths in a laboratory showed periodicity in the liberation 

 of their sexual organs, and behaved in every way in exactly 

 the same manner as if they had been in the sea. This 

 evidence is considered to indicate that periodicity is a 

 heriditary character. 



No periodicity is manifested by those plants bearing 

 tetraspores or asexually-produced reproductive bodies. 



Dispersal of Seeds a.nd its Bearing on 

 the Geographical Distribution of Plants. 



Dr. Ridley, ot the Bont.iiiic tjardens, Singapore, has been 

 studying the rate of dispersal of seeds by wind. They are 



