January 25, 19 12] 



NATURE 



423 



where I is the mean free path of the molecules of the gas 

 divided by the radius of the sphere. It will be seen that 

 the result involves an exponential term not given by the 

 theoretical investigation of Cunningham or the experi- 

 mental work of McKeehan, although the authors show that 

 there is some indication of its effect even in the observa- 

 tions made by the latter. 



A LECTURE, under the auspices of the Graham Lecture 

 Fund was delivered on Tuesday, January i6, in the hall 

 of the Technical College, Glasgow, by Prof. H. E. Arm- 

 strong, F.R.S. The lecture was arranged by the Royal 

 Philosophical Society, and the subject selected was " Some 

 Consequences of Graham's Work." The lecturer was 

 dealing with a subject on which he was specially qualified 

 to speak when he described the way in which Graham's 

 work on diffusion had been developed in recent years. The 

 effects produced by non-electrolytes, which are able to 

 penetrate the membranes of living cells, and so to set 

 going important physiological processes, are now recog- 

 nised as factors of vital importance in the life and develop- 

 ment of plants and animals ; it was therefore a happy 

 inspiration on the part of the trustees of the Graham Fund 

 to secure from Prof. Armstrong himself a description of 

 the experiments which have done so much to bring home 

 to the physiologist, as well as to the chemist, the important 

 results which have followed upon the pioneer work of 

 Graham. 



An interesting study of the localisation and function of 

 potassium in plants, by Dr. Th. Weevers, is contained in 

 the Recueil des Iravaux botaniques Neerlandais (vol. viii., 

 p. 289), use being made of Macallum's very delicate micro- 

 chemical test, based on the precipitation of potassium 

 cobalt nitrite and subsequent conversion of this into black 

 cobalt sulphide by treatment with ammonium sulphide. In 

 a very large number of plant tissues tested, potassium was 

 found always to be present, save in the Cyanophyceae. In 

 all cases the cell nucleus, however, contained no trace of 

 this element, even in cases when the cytoplasm contained 

 this element in abundance. Special experiments showed 

 that this result was due neither to potash salts diffusing 

 out of the nucleus under the treatment, nor to inability of 

 the reagent to penetrate therein. -The larger portion of 

 the potassium is contained in the vacuoles of the cells, the 

 chromatophores being free from it ; chlorophyll also con- 

 tains no potassium. In all cases tested the potassium was 

 present in a form soluble in water, and can be extracted 

 practically completely from the cell by water or 50 per 

 cent, alcohol, but it seems to be insoluble in ether. In 

 phanerogamous plants the potassium is most abundant in 

 the parenchyma, especially in the growing points and re- 

 serve organs. In the secondary tissues potassium pre- 

 dominates in the living elements of the wood and bark, 

 especially in the cambium and medullary rays ; the latter 

 sf>cm to act as potash reserves for the growth of new 

 shoots. In discussing the physiological significance of 

 potassium in the plant, it is considered that this element 

 plays little or no part in carbon assimilation, but probably 

 is concerned more in building up protoplasm at growing 

 points. In the leaf it probably functions in synthesis and 

 degradation of the protein. 



Messrs. Witherby and Co. are about to publish " The 

 Game-birds of South Africa." The book is by Major 

 Boyd Horsbrugh, and will be illustrated by nearly seventy 

 coloured plates reproduced in facsimile from the drawings 

 of Sergeant C. G. Davies. The work will be in small 

 quarto, and will be issued in four quarterly parts. 



NO. 2204, VOL. 88] 



OUR ASTRONOMICAL COLUMN. 



Sciiaumasse's Comet, 191 i/i. — In the Comptes rendus 

 for January 8 (No. 2) M. G. Fayet announces his tentative 

 conclusion that the comet discovered by M. Schaumasse 

 at Nice on November 30, 191 1, is a periodic comet with 

 a period of about seven years. A parabolic orbit first 

 calculated showed such digressions from the observed 

 places that an elliptic orbit was tried which gave satis- 

 factory O-C differences for intermediate positions. The 

 preliminary elements, determined from positions observed 

 at Nice on December i, 11, 16, and 21, 1911, are as 

 follows : — 



T =1911 November 12-2440 M.T. Paris. 

 ^ =136° 33' 37"] 

 a = 93° 14' 32" j- 1911-0 

 t = 17^ 40' 46"] 

 log (/ =0-084487 

 e =0-675480 

 M =489 "938" 



The data are, of course, too meagre for any certainty 

 to be claimed for these elements, but it is worthy of notice 

 that on December 28 the departure of the observed place 

 from M. Fayet 's ellipse was only 15". 



The Distribution of Brightness in the Tail of 

 Halley's Comet. — Some important results concerning the 

 nature of the particles in the tail of Halley's comet, and 

 of their illumination, are obtained by Drs. Schwarzschild 

 and Kron in a paper of which a translation is printed in 

 No. 5, vol. xxxiv., of The Astrophysical Journal. The 

 material for the discussion was provided by plates secured 

 by the Potsdam Observatory expedition to Teneriffe to 

 observe the comet. 



The photographs were secured in pairs, and photometric 

 standards for comparing the density of the image were 

 produced simultaneously ; the photographs show that the 

 apparent intensity of the tail diminishes continuously from 

 the head outward. This diminution might be produced by 

 two causes, first the decrease in density of the tail matter, 

 secondly by a decrease in the actual luminosity of the 

 individual particles ; decrease in density would be pro- 

 duced by increase in cross-section of the tail as units 

 further from the head were considered, and by the greater 

 velocity of the particles through each section produced by 

 the solar acceleration. 



The density effect was very carefully calculated by the 

 authors, and, to their surprise, was found to account, in 

 the most part, for the decrease of brightness. It should 

 be remembered, however, that several unknown quantities 

 enter into the conditions discussed. This result, if legiti- 

 mate, can be explained by assuming that the light of a 

 comet's tail is a kind of fluorescent or resonant radia- 

 tion excited by the solar radiation. On this basis they 

 calculate the amount of matter passing through a unit 

 section, and also the density, and find that, exposed for a 

 whole day to the conditions obtaining at the time of its 

 passage through the tail, the earth would not collect more 

 than 250,000 kilograms of cometary matter, a relatively 

 insignificant amount. 



Observations of Planets.— In No. 4548 of the Aitro- 

 nomische Nachricbtcn i^ piililishinl a telegram, received 

 from Prof. Lowell on Jimi.uv 12, announcing that since 

 the last presentation the canal Titan on Mars has doubled. 



M. Jarry-Desloges reports that the south polar cap re- 

 appeared, as two distinct masses, on January 3, and that 

 the abnormal white streak at the north j>oIe going south 

 between Propontis and Palus Mxotis, had completely dis- 

 appeared on that date. 



The latter also states that on December 29, 191 1, at 

 23h. 3oni., the south polar regions of Saturn were covered 

 by a well-defined dark area having an equally well-defined 

 greyish area at its centre ; taking the equatorial diameter 

 of the planet as unity, the respective diameters of these 

 patches were 031 and o'> \i ?3h. 15m. the same even- 

 ing the eastern anterior f the rings appeared very 

 notably darkened, but nomenon did not endure 

 more than twenty-four hours, fhe farther pastern section 

 of the exterior ring, as compared with the Cassini division, 

 was also darkened. At this time tho inmr trnnspaifnt 



