286 



NA TURE 



[July 21, 1898 



Lebedintseff and W. Krzyzanowski. — Geological explorations 

 along railway lines in South Russia, by V. Laskareff. — On the 

 sexual reproduction of Schiznnnira lanigera, by S. Mokrzecki 

 (with a coloured plate). — On the influence of substitution on the 

 rate of certain reactions, by P. Petrenko Krichenko. — Crangon 

 vulgaris, var. Shidlovskii, from the Sea of Japan, by Dr. A. 

 Ostroumoff. 



Vol. xxi. part i. — Materials for the fauna of Coleoptera of 

 South Russia, by E. Kubkovski. An elaborate work which 

 contains a review of the corresponding literature, a sketch of the 

 distribution of Coleoptera in the Steppes, the sandy regions, 

 the waters, &c. , and a detailed enumeration of the species. 



Memoirs of the Novorossian [Odtssd] Society of Naturalists^ 

 Mathematical Section, vol. xvii. — Solar radiation, by M- 

 Pantchenko. The author submits to a careful mathematical 

 investigation the different formulae proposed by VioUe, Langley, 

 Abney, Bartolli, Crova, Angot, and Angstrom. For purely 

 meteorological purposes he finds Angstrom's formula sufficient ; 

 it gives very good results with the actinometric measurements 

 made in Odessa in 1890, 1891 and 1894. 



SOCIETIES AND ACADEMIES. 

 London. 



Royal Society, June 16.— "On the Source of the Rontgen 

 Rays in Focus Tubes." By Alan A. Campbell Swinton. Com- 

 municated by Lord Kelvin, F.R.S. Received June 7. 



The author has already described at the Royal Institution 

 (see Nature for May 26, page 91) how he has found it 

 possible to study by means of pin-hole photography the active 

 area on the anti- kathode of a focus tube from which the Rontgen 

 rays proceed. 



By means of a special camera he has now been able to make 

 further investigations. In the illustration A is the pin-hole in a 



lead disc secured by a cap to the brass cone B, which is lined 

 with thick lead. D is a framework into which slides either the 

 fluorescent screen E, or a carrier containing a sensitive plate 

 should photographs be required, pis an observation tube for 

 use with the fluorescent screen. It is made of insulating 

 material to avoid danger of shocks. 



With this apparatus directed at the anti-kathode of a focus 

 tube, it is easy with the fluorescent screen in place to take 

 accurate note of the image of the active anti-kathode area which 

 appears on the screen, and to observe the variations in form, 

 dirnensions, and brilliancy that take place under varying con- 

 ditions. Similarly by replacing the fluorescent screen by a 

 photographic plate the image can be photographed. 



The following are the main effects that the author has 

 observed. 



(1) When the anti-kathode intersects the kathode stream at 

 the focus, the dimensions of the active area are independent of 

 the degree of exhaustion. For all other positions beyond the 

 focus it is larger the lower the exhaustion and vice versa. 



(2) When the anti-kathode intersects the kathode stream 

 beyond the focus, the active area is larger the greater the 

 distance between kathode and anti-kathode. 



(3) When the anti-kathode intersects the kathode stream con- 

 siderably beyond the focus, the active area is found to consist of 

 a well-defined and very intense central nucleus, surrounded by a 

 much fainter but quite appreciable halo. Both of these increase 

 in size as the distance between kathode and anti-kathode is 

 increased. In some cases the halo consists of a well-marked 

 hollow ring with a dark space between it and the central nucleus. 

 In other cases two distinct concentric rings are visible surround- 

 ing the nucleus. 



NO. 1499, VOL. 58] 



(4) With an anti-kathode inclined at an angle of 45' to the 

 axis of the conical kathode stream, it is found that those portions 

 of the stream which impinge most normally upon the anti- 

 kathode surface are considerably the most efficient in producing 

 Rontgen rays. 



(5) At the degrees of exhaustion most suitable for producing 

 Rontgen rays, and with concave kathodes of the usual dimen- 

 sions, the kathode stream proceeds almost entirely from a small 

 central portion of the kathode surface, the remaining portion of 

 the surface being apparently practically inoperative. That this 

 is so was very conclusively established by photographs taken 

 with a tube in which three very minute fragments of glass had 

 attached themselves on to the concave surface of the aluminium 

 kathode. The shadows of two of these fragments appeared in the 

 photographs, and enabled accurate measurements to be made. 



(6) The different portions of the kathode stream proceeding 

 from different portions of the kathode cross at the focus and 

 diverge in a cone that retains any special characteristics of the 

 convergent cone. The relative positions of the glass fragments 

 on the kathode, and the positions and enlargement of their 

 shadows on the anti-kathode were found to shoW this very 

 clearly. 



(7) Though by far the greater portion of the Rontgen rays 

 given by a focus tube proceed from the active anti-kathode area, 

 still a very appreciable quantity is also given off by all those 

 portions of the glass of the tube that shows the green fluor- 

 escence. 



Further, it is noticeable that that portion of the glass that 

 shows the brightest fluorescence, i.e. that part which lies in the 

 path in which kathode rays would be reflected frohi the anti- 

 kathode surface were they reflected according to the law of 

 equal angles of incidence and reflection — gives off the most 

 Rontgen rays, while those portions of the glass that show no 

 fluorescence do not give ofT any Rontgen rays. The conclusion 

 appears obvious that whatever produces the one also produces 

 the other, but as has been pointed out by Prof. S. P. Thompson 

 the fluorescence is not due to the direct 

 stream of rays from the kathode, but to 

 some description of radiation that pro- 

 ceeds from the surface of the anti-kathode 

 that faces the kathode. 



Prof. Thompson calls these radiations 

 " para-kathodic rays," stating that they 

 differ from the Rontgen rays in respect of 

 their power of penetration, and in their 

 capacity of being electrostatically and mag- 

 netically deflectable. In these respects the 

 author's experiments confirm those of Prof. 

 Thompson ; but when the latter goes on to 

 differentiate these rays from ordinary kathode rays, on account 

 of their not exciting Rontgen rays where they impinge on a 

 solid surface, the author is unable to agree, for, as above stated, 

 these rays do excite Rontgen ra^s where they impinge upon the 

 glass walls of the tube. 



The "para-kathodic" radiations do not, however, appear to 

 be ordinary kathode rays. In the first place they do not pro- 

 ceed directly from the kathode, but only from the surface of 

 the anti-kathode that faces the latter. Secondly, they do not 

 appear to be negatively but positively charged. The author sug- 

 gests that they may very probably consist of kathode ray particles 

 which, having struck the anti-kathode, and having thus given 

 up their negative charges and acquired positive charges, rebound, 

 both by reason of their elasticity and also by repulsion from the 

 anti-kathode. Perhaps, owing to the comparative roughness of the 

 anti-kathode surface, they fly off to some extent in all available 

 directions, but they do so especially in that direction which the 

 law of equal angles of incidence and reflection requires. It also 

 appears very possible that these rays are identical with the 

 positively electrified streams proceeding from the anode, which 

 the author has investigated by means of radiometer mill wheels, 

 recently described in his paper to the Physical Society (see 

 Nature for March 31 and June 2, pp. 525 and 119. 



" Mathematical Contributions to the Theory of Evolution. 

 V. On the Reconstruction of the Stature of Prehistoric Races." 

 By Karl Pearson, F.R.S., University College, London. Re- 

 ceived June 6. 



The object of this memoir is to illustrate the general theory 

 by which we may reconstruct from the knowledge of one organ 

 in a fossil or prehistoric race, the dimensions of other organs, 

 when the correlation between organs in existing races of the 



