July, 1913. 



KNOWLEDGE. 



265 



the fact that the two very distant stations agree in the days 

 that give unusually high or low values. 



High radiation values are accompanied by a relative 

 increase in the strength of the violet radiations, and conse- 

 quently increased contrast between the centre and edge of the 

 Sun's disc. From this they conclude that the variation is 

 actually in the Sun, and not due to the interposition of a 

 meteoric screen. Haze was very prevalent in 1912 : it is 

 supposed to have been caused by the presence of fine dust in 

 the air, from the eruption of Mt. Katmai in Alaska. When 

 this is allowed for, the radiation of 1912 is higher than that of 

 1911. Hence the cause of the abnormally hot summer of 

 1911 is to be sought on the Earth, not in the Sun; but the 

 Katmai dust may have had something to do with the cold 

 summer of 1912. 



BELTS ON NEPTUNE. — The same number contains a 

 series of drawings of Neptune made by Professor T. J. J. See 

 in 1899. They clearly show a number of curved dark belts on 

 each side of the Equator, where there is a narrow bright 

 streak. These drawings were made before the position of the 

 Equator had been deduced from the shift of the node of the 

 satellite's orbit, and it is interesting to note that the Equator 

 in the drawings is not in the plane of the satellite's orbit, but 

 inclined to it about 20°, which agrees with theory. Belts on 

 Uranus were seen by Mr. Buffham, Professors Young and 

 Schiaparelli and the Henry brothers. The four giant planets 

 seem to be all alike in this respect, as in low density and rapid 

 rotation. 



THE SELENIUM PHOTOMETER.— A posthumous 

 paper by Professor Ristenpart describes an application of 

 the selenium photometer to the measurement of the diminu- 

 tion of light in the solar eclipse of last October. The time of 

 minimum light is very sharply defined, the curve on each side 

 being very steep ; while this particular research is more orna- 

 mental than useful, it illustrates the power of the method, 

 which depends on the increased electrical conductivity of 

 selenium when light falls upon it. 



SCHAUMASSE'S COMET.— The following are improved 

 elements of this comet : — 



Perihelion passage, 1913. May 15-1648, Paris M.T., Omega 

 53° 2' 17", Node 315° 5' 25", Inclination 152° 21' 23", 

 Log Perihelion Distance 0-163514. 



Ephemeris for midnight, July 3, R.A. 13" m 12 s , N.Dec. 28° 34' ; 

 July 7, R.A. 12 h 52 m 7 s , N.Dec. 26° 56'; July 11, 

 R.A. 12 h 45"' 50 8 , N.Dec. 25° 29' ; July 15, R.A. 12 h 41 m s , 

 N.Dec. 24° 11'. 



NAMES FOR THE units of planetary and stellar distances 

 are suggested by Mr. J. W. Scholes. He gives Parxsecarc for the 

 stellar unit. This is like the " Parsec " suggested by Professor 

 Turner. " Disethsun " is suggested for the distance Earth- 

 Sun ; for myself I should have thought the term " Astron " 

 very suitable for this, if not used for the stellar unit. For it is 

 an obvious abbreviation of Astronomical unit of length, which 

 has hitherto been the term used. 



CONGRATULATIONS to Sir J. D. McClure on his 

 knighthood. There must be many of our readers who have 

 heard his lectures on astronomy, which were prepared with the 

 most conscientious care and zeal for accuracy, and whose 

 illustrations, both pictorial and verbal, were calculated to 

 arrest and sustain the interest of his hearers. 



OBITUARY.— I have heard with regret of the death of Mr. 

 F. W. Henkel, who was a familiar figure at astronomical 

 meetings and an occasional contributor to this magazine. 

 Also of Professor Luis G. Leon, the energetic Secretary of the 

 Mexican Astronomical Society. He made its journal a most 

 readable summary of astronomical progress ; he visited 

 Greenwich a few months ago, and published an interesting 

 account of his impressions. 



BOTANY. 



By Professor F. Cavers, D.Sc, F.L.S. 



ANTARCTIC LICHENS.— In his report on the lichens of 

 the Swedish Antarctic Expedition (Wiss. Ergcbn. Schwed. 

 Siidpolar-Exped., Band 4, 1912) Dr. Darbishire gives some 

 interesting details regarding the distribution of lichens gen- 

 erally in the Antarctic and Arctic regions. Up to the present 

 one hundred and five lichen species are known from the land 

 lying strictly within the Antarctic limits, and of these thirty- 

 two occur also in sub-Antarctic America, twenty-five in New 

 Zealand, and sixteen in South Georgia, showing a very close 

 affinity between the Antarctic lichen flora on the one hand 

 and the American and New Zealand lichen floras on the 

 other, the difference to the disadvantage of the latter being 

 accounted for by the greater nearness of the sub-Antarctic 

 American region to the extreme limit of the southern drifting 

 pack-ice. The lichens of sub-Antarctic America and New 

 Zealand are also very closely allied ; for out of the one 

 hundred and thirtythree lichen species of the former Mora, 

 one hundred and thirteen are found in New Zealand, thirty- 

 two in the Antarctic, and thirty-one in South Georgia, the 

 latter being evidently, from the phytogeographic point of 

 view, a half-way house on the road from sub-Antarctic 

 America to the Antarctic area. Moreover, about half of 

 the Antarctic species occur also in the Arctic regions. 



Of the one hundred and six Antarctic lichens, sixty-nine are 

 crustose (encrusting forms which are applied so closely to the 

 rock that the latter has to be chipped off in order to get 

 specimens of the lichen), eighteen foliose (attached to the 

 surface at various points on the underside of the thallus, but 

 more easily removed than the crustose forms), and nineteen 

 fruticose or shrub-like (attached only at one point) : of these, 

 the numbers found in sub-Antarctic America are respectively 

 sixteen, five, and eleven. Of the sixty-seven species found 

 only in the true Antarctic area and nowhere else, forty-nine 

 are crustose, ten foliose, and 8 fruticose. The sub-Antarctic 

 American flora includes three hundred and six lichen species, 

 while seven hundred and forty have been found in New 

 Zealand : of the species common to the two regions fifty per 

 cent, are fruticose, thirty per cent, foliose, and only twenty 

 per cent, crustose. The affinities of the lichen floras of 

 sub- Antarctic South America and New Zealand lie mainly in 

 the fruticose lichens which are the oldest and probably the 

 least variable forms. The encrusting lichens are more 

 variable and have adapted themselves more readily to local 

 conditions, thus giving rise to new species. 



Dr. Darbishire raises the interesting question of the re- 

 sistance to cold by lichens, and suggests some experiments 

 which might be made on these plants in the coldest regions. 

 For instance, it would be interesting to determine the amount 

 of water contained in the lichen thallus at different times and 

 seasons ; in what condition the lichens exist during the long 

 winter ; at what temperature assimilation begins, and so on. It 

 is of little use to make experiments on the plants in warmer 

 climates if we wish to ascertain how these lichens can live 

 under the adverse conditions prevailing in the polar regions. 

 Lichens are found everywhere on the outer limits of vegeta- 

 tion, and their chief ecological factor is their power to become 

 quite dry and yet remain alive. No doubt it is this power 

 which enables them to spread slowly but surely into the 

 bleakest and most inhospitable regions. They are making 

 their way towards the North and South Poles, and so far have 

 been beaten in their race only by the perpetual covering of 

 snow. If bare rocks are found in the neighbourhood of the 

 Poles themselves there is little doubt that lichens will be 

 found growing there. 



VEGETATION OF NATAL.— An extremely interesting 

 account of the vegetation of Natal is given by Professor J. W. 

 Bows in the Annals of the Natdl Museum, II, 1912. 

 From the coast to the Drakcnsberg range, Natal presents 

 three terraces (about three hundred, six hundred and one 



