64 



KNOWLEDGE & SCIENTIFIC NEWS. 



[March, 1907. 



ASTRONOMICAL. 



By Charles P. Butler, A. K.C.St. (Lond.), F.R.P.S. 



Silicon in the Chromosphere. 



In a paper recently communicated to the Royal Astronomi- 

 cal Society, Professor A. Fowler discusses the evidence he 

 has collected for the identification of two strong red lines ol 

 silicon with well-marked chromospheric lines. Careful 

 determinations of their wave-lengths from ■■■■ photographic 

 spectrum of high dispersion give the values 1^47. .;i and 

 6371.57. The more refrangible line is the stronger in the 

 proportion of 10 to (1, while their intensities in (lie chromo- 

 sphere arc 25 and 15 respectively. There ma; have been 

 some suspicion of duplicate origin with a line ol iron re- 

 corded by Kayser and Rumge al \ 6371.60, but il there is 

 such an iron line it is certainly nol an enhanced line. From 

 other considerations ol the behaviour of the line ii appears 

 mosl satisfactory to attribute it chiefly to silicon. In hih- 

 spol spectra these two lines are almost obliterated, and this 

 feature is in accordance with the general behaviour of 

 chromospheric lines. These two silicon lines show the 

 general characteristics ol i nlianced lines in that they appear 



iK.sr 10 the positive pole ol ihe .ire. — (MontMy Notices, 77. 

 p. 157, December, moo.) 



The Sun's Spotted Area during: 1905. 



In reviewing the measures of sun-spots for the year 1905 

 from photographs taken at Greenwich, Dehra Dun, Kodai- 

 kanal and Mauritius, the Astronomer-Royal stales thai there 

 was a marked increase over the area for 1904, both the 

 umbras and the whole spots showing an increase ol over 

 144 per cent., the actual area of 1191 being greater than 

 that of 1 yy ^ . Three periods of exceptional activity were 

 noticeable, comprising Januar) to March, July and October 

 to November. The faculae, as usual, maintained a mote 

 steady rate of advance than the spots, the total for the whole 

 year only showing an increase of 48 per cent, over thai for 

 1904. The two hemispheres showed different activities in 

 the ratio of 63 to 37, for the north and south respectively. 

 As the mean distance from the Equator of all spots barel} 

 exceeded 1 ;''. this is suggestive that 1905 was the actual 

 Mar of maximum of the present cycle. Also every latitude 

 from the Equator up to 32 was represented, this being an 

 arrangement usually characteristic of the year of maximum 

 activity. The most striking feature of the year was the 

 great number of abnormally large spot groups, notably that 

 ol January 29 to February 11, 1905. 



Rotation of Giacobini's Comet C. 1905i. 



In the case of Swift's Comet [892 I., Professor W. II. 

 Pickering brought forward evidence to show that its tail 

 exhibited a rotation about its axis in a period of about four 

 days {Harvard Annals 32, p. J71). After discussing recently 

 the beautiful photographs of Giacobini's comet of [905 ob- 

 tained by Professor I-;. I';. Barnard, Pickering finds thai they 

 are divisible into two main (lasses, in one of which the tail 

 is narrow, and in the other broad, giving the impression of 

 a sword alternately presenting to us its edge and its flat 

 side. In this case the rotation was somewhat slow, and as 

 tin' comet was only visible for a short lime, the photographic 

 evidence only exists through a range of fifteen days. The 

 intervals between the two presentations is about nine days, 

 so that the period of rotation would be eighteen days. Pro- 

 fessor Pickering makes the appeal that all future comets 

 should be photographed as frequently as possible, so that 

 any changes may be more accurately determined. 



Perturbations of Halley's Comet. 



In view ol the general interest taken in the approaching 

 apparition of Halley's periodical comet, Messrs. Cowell and 



Crommelin have undertaken the computation of the per- 

 turbations. Wishing to obtain a preliminary survey as to 



ii i redness ol Pontei oulant 's perihelion date, they have 



made a compulation of tin Jupiter perturbations, dividing 

 iln comet's orbit into cight\ portions, and following Ponte- 

 coulant's method closely. The two main results of this in- 

 quiry are : ( i i May, K|io, is the correel dale within a month 

 for the next perihelion passage. Their actual date is a fort- 

 night earlier than Pontecoulant's, bill no stress is laid on 

 ibis difference. (2) Pontecoulant's value ol the eccentricity 

 lor !i)ii) is notably in error, the perihelion distance being 

 practically the same as al Ihe last return (0.59), whereas he 

 increased il to (0.68). This change is of importance, as it 

 would considerably affect the geocentric path of the comet 

 al Ihe next return, and would considerably modify the point 

 at which the meteors accompanying the comet would inter- 

 sect the earth's orbit. 



Exploration of the Upper Air. 



Extraordinary heights have been attained l>\ registering 



balloons in connection with ihe work undertaken at various 

 stations tor the International Committee for researches in 

 the upper air. On July 6, 1905, a rubber balloon sent up 

 from the Meteorologische Zentralstation at MUnchen 

 (Munich) attained a height of 23,000 metres (14.292 miles). 

 The balloon was 1 '■ metres diameter, inflated with hydro- 

 gen. It landed at Deggendorf, having travelled a distance 

 of_ iji kilometres W.N.W., the period of flight being 97 

 minutes. 



BOTANICAL. 



By G. Massee. 



The Water Hyacinth. 



Tins beautiful aquatic plant, known botanicall;, as Eichoriiea 

 speciosa, is at the present moment a source of great anxiety 

 to the members ol the Legislative Assembly of New South 

 Wales, owing to its rapid extension in the creeks, lagoons, 

 and more sluggish rivers of that country, thus impeding 

 navigation. When growing in shallow streams or lagoons, 

 it tends to suck up the water, and converts limpid streams 

 into bogs. The plant is a native of tropical South America, 

 and, being very showy, is much cultivated. Its spread in 

 New South Wales is traced to a few plants having been 

 thrown into Swan River by a local resident, who cultivated 

 it as a decorative plant. The water hyacinth is an aquatic, 

 and usually floats freely without being attached to the soil ; 

 when growing in shallow water or swamps the roots grow 

 into the mud. If the mud becomes dry, the plant perishes. 

 The leaves are roundish and arranged in a dense rosette 

 one or two feet high ; the lower portion of the leaf-stalks 

 are much swollen and tilled with air, and serve as buoys 

 insuring the stability of the plant, and preventing its being 

 overturned by wind or waves. The roots form a dense tuft 

 one or two feet long. The flowers are produced in pro- 

 fusion, of a lilac colour, and arranged in clusters like those 

 of the hyacinth, hence the popular name. The plant is re- 

 produced abundantly by stolons or shoots from the parent 

 stem; these stolons, when about six or nine inches long, 

 form a rosette of leases at tin tip, which soon forms a 

 plant as large as the one from which it originated, and in 

 turn produces stolon-, ; |,y such means dense groups of plants 

 of different generations remain organically united, and as 

 the stolons are very strong, rowing boats and barges find 

 it impossible to make headway, ami steamers fare but little 

 better, as the plants become entangled in the blades of the 

 propeller. During floods large masses of the weed are de- 

 tached and carried down stream as floating or half-sub- 

 merged islands, which prove dangerous to bridges, jetties, 

 &c. No satisfactory means of destroying the plant have as 

 vet been devised. Some years ago certain rivers in Florida 

 were completely choked up with this plant, which had been 

 accidentally introduced. Specimens of the plant are at pre- 

 sent growing in the Lily House, Kew Gardens. 



