February 28, 1895] 



NATURE 



423 



Some time ago we ga»e an account of the considerable 



extension of the ultra-violet photographic spectrum obtained 

 by Dr. Victor Schumann, of Leipzig, by eliminating the air 

 between the so urce and the sensitive plate, which was found to 

 €xert a strong absorption upon the rays of shortest wave-length. 

 This work has been carried on since with great success. At a 

 recent meeting of the Vienna Academy, Dr. Schumann 

 announced that he had improved his plates and his " vacuum 

 spectrograph" so as to obtain results in a few minutes which 

 used to take as many hours. The hydrogen spectrum shows a 

 further lengthening, and the spectra of cobalt, iron, aluminium, 

 zinc, and cadmium have also been considerably extended 

 beyond 170 ^;U. This limit, although far beyond the ordinary 

 limits of the photographic spectrum, was due to a residue of 

 air and electrode vapour. The absorptive effect of air upon 

 the most refrangible rays was traced down to thicknesses below 

 O'Ol mm. Hydrogen also shows a strong absorption for these 

 extreme rays, especially if insufficiently dried. 



Herr K. Mack, working in the Hohenheim Physical Insti- 

 tute, has succeeded in demonstrating the occurrence of double 

 refraction of electric waves in wood. That electric waves, un- 

 like light waves, are capable of penetrating wood, was already 

 found by Hertz. " It is not without surprise," he says in his 

 classical work on the "Propagation of Electric Force," "that 

 one sees the sparks appear inside a closed room." But the 

 fact that waves of electric force are transmittc<l in a different 

 manner accordingly as they vibrate across or along the fibre of 

 the wood, has only just been proved by Herr Mack, who gives 

 a full description of his method in the current number of 

 IVieil'.manits Aittialen. It is well known that two NicoU 

 prisms transmit no light when their principal planes are crossed, 

 but that light may be made to appear by inserting a doubly- 

 refracting substance between them. For the Nicoll prismssub- 

 stitute Hertzian concave mirrors with their focal lines crossed, 

 and, instead of the tourmaline or other doubly-refr.iciing sub- 

 stance, insert a plate of wood 10 inches thick, with its fibre at 

 45° to each of the focal lines, and you have Mack's apparatus. 

 The sparks, which are extinguished on crossing the two focal 

 lines, reappear on inserting the wood in the manner indicated. 

 This striking experiment form; another important link in the 

 chain connecting the domain of light with that of electiicity. 



IfJ an admirable paper on the after-shocks of earthquakes 

 lyournal of the College of Science, Imperial University of 

 Japan, vjI. vii. part ii.), Mr. F, Omori has attacked a some- 

 what neglected branch of seismology. In three recent 

 Japanese earthquakes, those of Kumamoto in 1S89, Mino- 

 Owari in 1891, and Kagoshima in 1893, the after-shocks have 

 been carefully recorded, and are here specially studied from the 

 frequency point of view. Numerous tables are given, and also 

 many curves showing the way in which the number of after- 

 shocks varies with the time at different places. When their 

 inequalities are smoothed away, these curves differ little from 

 rectangular hyperbolas. At the same time, they show periodic 

 6uctuations in the decrease of frequency of after-shocks. Be- 

 sides the diurnal and annual fluctuations, six different periods 

 have been ascertained, whose lengths range from a few hours to 

 several months. In the case of the great Mino-Owari earth- 

 quake of 1891, the after-shocks were most numerous some dis- 

 tance to the south of the principal epicentral tract, which lay 

 in the Neo valley. They also occurred more frequently along 

 four axial lines, r.adiatinj from the vicinity of KoDri, th.an in 

 the neighbouring districts. Mr. Omori suggests that the 

 principal earthquake was caused by the formation of some great 

 fractures beneath the Neo valley, and that the axial lines 

 indicate the positions of four weaker or deeper fractures, along 

 which the crust is not yet in the way of steadily settling into 

 equilibrium. 



NO. 1322, VOL. 51] 



In a paper recently published {fournal of Geology, May- 

 June 1894 ; Johns Hopkins University Circular, January 

 1895), Prof. W. K. Brooks discusses from the zoological point 

 of view a problem familiar to the geologist — the sudden appear- 

 ance in the Lower Cambrian of a rich fauna in which most of 

 the great classes of animals are represented by unmistakable 

 forms. His conclusion is that early Cambrian times and those 

 immediately preceding them formed a period of rapid modifi- 

 cation induced by the first colonisation of the sea-bottom. His 

 arguments maybe briefly summarised thus : — Embryology indi- 

 cates simple pelagic forms, as the ancestors of all the great 

 animal stems. The existing pelagic fauna consists in part of 

 small and primitive forms, and in part of the specialised de- 

 scendants of shore or bottom forms. The fact that the latter 

 are almost exclusively carnivorous indicates the enormous 

 wealth of plant-life, mostly of minute forms, on which ulti- 

 mately the existence of all the fauna depends, and shows the 

 extremely favourable character of the conditions of pelagic life 

 to simpleorganisms. The supply of these simple organisms is in- 

 exhaustible, and on themthe bottom-fauna also depends for food. 

 It is suggested that the evolution of all the main stems of animal 

 life took place at tlie surface of the ocean, but that when their 

 descendants had colonised the bottom the crowding that soon 

 ensued there led to fierce competition, especially between nearly 

 related forms, and to the specialisation of the types already 

 established, but not the production of new types. Tfie develop- 

 ment of hard skeletons was an early result of these conditions. 

 Geologists will certainly find many points to criticise in Prof. 

 Brooks's sug'^estions, but they constitute an important addition 

 to the discussion of faunal origins. 



One of the many botanic stations the advancement of which 

 has been promoted by the Director of the Royal Gardens at 

 Ke«-, is that at Aburi on the Gold Coast. A few interesiing 

 facts referring to the est.-iblishment and present condition of this 

 station are given in the Keiv Bulletin for January, from 

 which the following information has been gathered. The site 

 is in the hills, .-it an elevation of about 1400 feet, overlooking 

 the sea-board, near Accra and Pram Pram. In addition to its 

 suitability for the growth of economic plants, Aburi is a valuable 

 resort for European invalids. The locality has been greatly 

 improved of late years, and it promises to become the centre of 

 activity for many cultural industries started by the Botanic 

 St.^.tion. During the winttr of 1893-94 Mr. William Crowther, 

 the curator (appointed in 1S90), was deputed to visit the West 

 Indies "to observe the system pursued there in the cultivation 

 of economic plants, and to bring back such useful seeds and 

 plants as might with advantage be introduced to the Gold 

 Coast." Mr. Crowther very successfully carried out the object 

 of his mission, and published a delaileil report. Since then the 

 work of the .Vburi Station has made excellent prepress. The in- 

 ception, as well as the actual work, so far accumplished in 

 botanical enterprise at the Gold Co.ist, is entirely due to the 

 Governor, Sir W. 1!. Griffith. He has given warm .and con- 

 sistent support to the station, and personally encouraged in 

 every vv.ay the efforls of the cur.ator. 



The Forsckungsherichte ( Theil .3, 1895^ of the biological 

 station at Pliin, recently published, contains a number of 

 interesting papers on the flora and fauna and on the biological 

 phenomena of ihe lakes adjoining the station. Among the 

 contents may be mentioned the copious reports on the flora by 

 Drs. Klebahn and Lemmermann, the faunistic contributions of 

 Dr. Zacharias, and the memoirs of Drs. iiacharias and 

 Strodtmann on the Plankton of the lakes. The investigation 

 of the movements, periodicity, and changing quantity of 

 floating organisms in inland- waters can be pursued with such 

 ease and completeness, as compared with marine phenomena. 



