September, 1906.] 



KNOWLEDGE & SCIENTIFIC NEWS. 



541 



apparatus, in which the chief feature is the attempt at elimina- 

 ting friction and consequent distortion. A two-slit spectro- 

 graph, of any form, is mounted so as to move round a hori- 

 zontal axis perpendicular to the plane containing the optical 

 axis of the combination. The motion of the apparatus is pro- 

 duced by a Brashear clepsydra, mounted vertically. This is 

 connected with the spectrograph by means of a bar with 

 pointed extremities, which enter into two conical holes, one of 

 which is on the spectrograph in the prolongation of the optical 

 axis of the collimator, while the other is at the end of the 

 piston rod of the clepsydra. The axis of rotation of the spec- 

 troheliograph must pass through the point of intersection of 

 the axis of the collimator and that of the telescope of the spec- 

 trograph. The distances between this axis and the two slits 

 should be in the ratio of the focal lengths of the collimator and 

 telescope objectives. If a grating is employed (and the recent 

 discovery by Hale of the existence of dark hydrogen flocculi 

 has shown the advantage of the greater dispersion given by a 

 grating spectrum) the second slit may be stationary, and 

 placed in the axis of the telescope ; the setting on the spectral 

 Ime can then be accomplished by a slow rotation of the 

 grating. At its two extremities the secondary slit is widened 

 for the purpose of taking a photograph of a portion of the 

 spectrum of the diffuse light of the sky, thereby providing a 

 simple means of determining the exact radiation with which 

 the monochromatic photograph is to be obtained. A photo- 

 graphic plate may be placed immediately behind the secondary 

 slit, supported by the stationary base of the instrument (Hale's 

 arrangement), or the image may be photographed with a 

 separate camera (liSraun's arrangement). In this latter case 

 the image may be enlarged or otherwise at will. This form of 

 spectroheliograph may be arranged to receive light from a 

 siderostat or a coelostat, or it may be attached directly to an 

 equatorial. — Astropbysical Journal, July, igo6. 



Observations of the Zodiacal Light. 



Mr. Maxwell Hall has been making minute observations of 

 the zodiacal light for many years past at Kempshot, in 

 Jamaica, and, in a recent communication to the Monthly 

 Wi-athcr Rt'vic2r, he brings together most of the observations 

 and discusses them. His first series of tables show the esti- 

 mated breadth of the phenomenon at varying angular distances 

 from the sun. In the hope of obtaining additional information 

 he employed a spectroscope on the subject, but he says that no 

 bright or dark lines could be detected ; its spectrum — what 

 there was of it — was continuous, and coincided with the 

 brightest part of the solar spectrum, being for all practical pur- 

 poses apparently identical with the spectrum of twilight. 

 Further work with a specially designed spectroscope only con- 

 firmed the view that the zodiacal light was reflected light from 

 the sun. Close examination of many measurements of the 

 breadth indicated that instead of the light being bounded by 

 straight lines from the horizon upward these boundaries were 

 curved very perceptibly. 



The author next groups the observed latitudes of the various 

 parts of the glow with respect to their longitudes or distances 

 from the first point of Aries. In the resulting table there is 

 certainly a suggestive symmetry, and further inquiry shows 

 that the zodiacal light does not follow the ecliptic as has long 

 been supposed from casual observation, but that it closely 

 follows the invariable plane of the solar system. This plane 

 not only has a mathematical conception, but it may also be 

 regarded as the original plane of the solar system, throughout 

 which was scattered all the luatter subse([uently condensed 

 into the sun and planets. Employing the more recently de- 

 termined values of the masses of the planets, the value found 

 lor this invariable plane is — 



Inclination to ecliptic ... 1° 35' 2" ] , . 



Longitude of ascending node io5' 52' 37" j ^ " '' 

 Tabulating now the latitudes of the zodiacal light with respect 

 to this plane, they are seen to agree very closely except at 

 longitude 238° ; it is thought that the discordance here may be 

 due to the brightness of the planet Venus interfering with the 

 observations. 



The observations made by Mr. Maunder in I^gypt about the 

 end of 1897 are discussed, showing the zodiacal light to be 

 parallel to the invariable plane, but some ij' to the north. 

 This is a tendency common to observations at all northern 

 stations, and a series of authentic observations at southern 

 stations would probably prove most useful. In conclusion. 



the author expresses the opinion that the invariable plane still 

 contains such a large quantity of meteoritic matter as to 

 reflect back the light of the sun in the form usually seen; also 

 that the '^ f^n^t-nscluin " or counterglow, may be due to the "full 

 moon phase " of these particles of matter, and that all the 

 observed irregularities of light are due to the irregularities in 

 the distribution of the matter. 



Meteorology at High Altitudes. 



Most of the information concerning the upper air has been 

 obtained by means of automatic meteorological recorders 

 attached to kites or balloons. On November 29, 1905, a kite 

 sent up from the Prussian Aeronautic Observatory at Linde- 

 berg attained the record altitude of 6,430 metres. The self- 

 regislering instruments carried by the kite showed that at that 

 height the temperature was — 25°, the temperature at ground 

 level being + 5^; the wind had a velocity of 25 metres per 

 second, that at the surface of the earth being only 8 metres 

 per second. Six kites were employed, having a total surface 

 of 27 metres, the length of line paid out being 14,500 metres. 

 —del et Tcrre. 



Astronomical Clocks. 



The astronomical clock is so important an instrument of the 

 observatory equipment that any radical improvement or altera- 

 tion appears to deserve special notice. The chief drawback 

 to the employment of a first-rate clock has naturally been the 

 expense, but much of this ditficulty has been eliminated by 

 the new offer of Messrs. E. Dent and Co. — a guaranteed in- 

 expensive observatory clock at practically one-quarter the cost 

 of the type of instrument which has hitherto been only available 

 to the larger institutions. The new clocks can be obtained 

 with cither 12-inch or lo-inch dials, are fitted with dead-beat 

 escapement and wood-rod second pendulum, and may be 

 rated to either solar or sidereal lime. If desired, electric 

 contacts can be fitted at a small additional cost for transit 

 work. By the kindness of Messrs. Dent we have been able to 

 examine the rate record of one of these clocks, checked every 

 morning by the standard Greenwich signal, and the variations 

 shown indicate a very satisfactory compensation. 



-j.j.j.j^^ 



BOTANICAL. 



]3y G. Massee. 



The Wild Flora of Kew Gardens. 



OuiTH n-ceiilly a special number of the Kcw IhitUtin 

 has been devoted to the wild Fauna and Flora of Kew 

 Gardens. As would be expected, intensive cultivation 

 has altered the general features of the ground, and 

 habitats at one time suitable for wild plants h.ave now 

 disappe;ircd. Flowering plants have suft'cred most in this 

 respect, and out of the 422 species listed, many have now- 

 disappeared for ever. Among interesting mosses are Amhlfi- 

 steijinm Kuthii, known only from one or two counties in 

 England, Fissidcns crassipes and Hypnum dodes. Liver- 

 worts are very poorly represented in the list, although they 

 are known to have been more abundant years ago. but 

 unfortimatelv no early records nor specimens are forth- 

 toining. Lichens, as would be expected, on account of 

 their impatience of pure air, have practically disappeared, 

 only fifteen species being enunierated, and these are mostly 

 sterile. The paucity of members of the above-mentioned 

 groups is atoned for by the Fungi, which at the present day 

 number 378 genera and quite 2,000 species. The richness 

 of the Kiycologic Flora of the Gardens far surpasses in 

 point of numbers, as also in the variety of rare and interest- 

 ing species, any other record for an equal area. The richness 

 of the fungal flora will be more fuUv realised when it is 

 remembered that the entire British Fungus Flora consists 

 of 5,000 species, and that of Europe of 8,000 species. In (he 

 genus liiix.whi 53 species have been noted during the last 

 ten ve.irs, out of a total of 61 British species. The largo 

 size and brilliant colouring of most kinds belonging to this 

 genus render them very conspicuous objects in the arbore- 

 tiun ^luring late summer and early autumn. Fresh-water 



