88 



KNOWLEDGE. 



March, 1915. 



potassium chloride, or potassium bromide, vivid colours 

 are immediately produced. Common salt becomes yellow- 

 brown ; potassium chloride turns a beautiful violet ; 

 potassium bromide becomes a deep blue colour ; sodium 

 fluoride takes on a fine rosy tint. The colours so acquired 

 are permanent, if the specimens are kept in the dark at 

 ordinary laboratory temperature ; but in the daylight, and 

 also under heat, the colours gradually disappear until the 

 original white condition is again reached. SoUd solutions, 

 produced by fusing a small quantity of a colourable salt 

 with a great mass of a salt which itself remains colourless 

 in the kathode rays, acquire brilliant colours when subjected 

 to the rays, the colour assumed depending on the solvent 

 as well as on the solvend. Very small admixtures are 

 sufficient to produce intense colours. 



The first theory proposed to account for these effects 

 was that of Wiedemann and Schmidt, who regarded the 

 phenomenon as consisting in chemical reduction. Thus, 

 in the case of potassium chloride, the chlorine would be 

 set free, while the remaining potassium is dissolved in the 

 unaltered salt, which it colours. In support of this theory 

 Giesel coloured rock-salt by heating it in the vapour of 

 sodium or potassium. But the Giesel salts, although they 

 look like those coloured by the kathode rays, have quite 

 different properties in other respects. They do not fade 

 on exposure to light ; they give alkaline solutions, while the 

 kathode ray-coloured salts give neutral solutions ; the Giesel 

 salts do not give marked photo-electric effects, as do the 

 Goldstein salts. Finally, they are not phosphorescent, 

 while the Goldstein salts are. Goldstein has made salts 

 acquire all the properties of the Giesel salts by the pro- 

 longed action of kathode rays, the temperature of the salts 

 being allowed to rise during the bombardment. To these 

 salts, and to tho.se produced by Giesel, the theory of Wiede- 

 mann and Schmidt probably applies, while the explanation 

 of the Goldstein effects is that separation of the constituents 

 of the molecule occurs, but that neither constituent is 

 removed complete!}'. On this view the components remain 

 at quite small distances apart, and are thus ready to 

 re-combine. 



RADIO-ACTIVITY. 



By Alexander Fleck, B.Sc. 



DEFLECTION OF RECOIL PARTICLES.— It was 



mentioned recently in these notes that, when an a-particle 

 carrying a positive charge was liberated, the residual part 

 of the atom also acquired positive electricity. Just as a 

 gun starts travelling with a certain relatively small velocity 

 in the direction opposite to that of the discharged bullet, 

 so when an a-particle is sent off with a large initial velocity 

 the large part of the atom remaining recoils with a velocity 

 which, although small, is appreciable, and, as stated above, 

 with a positive charge. In the Februan,' number of The 

 Philosophical Magazine, \A'almsley and Jlakower describe 

 the behaviour of this recoil particle from radium-A when 

 it is subjected to a strong magnetic field. In such a field 

 ^-rays are completely deflected, and no trace of them is 

 found beyond the borders of the field, while the 7-rays are 

 not known to be influenced at all ; a-rays are deflected 

 slightly, and travel along the circumference of a circle of 

 large radius. It is found that the recoil particles also travel 

 along the circumference of a circle, of which the radius is 

 double that of the circle belonging to the expelled o-particles 

 deflected by the same field. 



GYROSCOPIC ATOMIC MODEL.— In the same journal 

 Dr. A. C. Crehore contributes a paper giving his views on 

 atomic structure. One great point of difference between his 

 model and the more generally accepted Rutherford model 

 is that, whereas the latter supposes that the positive charge 

 is concentrated on a very small nucleus in the centre of the 

 atom, this gyroscopic model suggests for the distribution of 

 the positive electricity a sphere of which the diameter is of 

 the order of 10-'" centimetres, and within which the elec- 

 trons vibrate, their " enormous frequency of orbit revo- 

 lution " confining them to one plane. It is not possible to 



discuss fully this theory here, but one point may be raised. 

 Dr. Crehore deduces from his hypothesis that " beta-particles 

 may come from any electron in the atom. ... In the 

 central nucleus theon,' they cannot come from the outside 

 rings, and must be restricted to the inner electrons or the 

 nucleus itself." 



It has been proved, however (Journal of the Chemical 

 Society, 1914, Volume CV, page 247), that the /3- particles 

 are entirely different from the majority of the electrons 

 which are present in the atom, and the number of which can, 

 in many cases, be altered by chemical means. In this 

 respect at least, therefore, the gyroscopic model is not so 

 satisfactory as the theory which supposes the atom to 

 consist of a nucleus surrounded bv a ring, or by rings, of 

 electrons. 



ZOOLOGY. 



By Professor J. Arthur Thomson, M.A., LL.D. 



GIGANTIC CUTTLEFISH. — C. Ishikawa and Y. 

 Wakiya describe the partly digested remains of a gigantic 

 Squid from the stomach of a Sperm Whale. The mantle 

 alone seems to have been about four feet in length. It is 

 probably Moroteuthis robusta, which has been captured 

 only twice before — by Dall and by D'Arcy Thompson. 



MYRMECOPHILOUS ORGANS IN A CATERPILLAR. 

 — In the caterpillar of Lycaena orion there are two kinds of 

 structures adapted for the attraction of ants. They have 

 been carefully described by Ehrhardt. When the cater- 

 pillar is touched by an ant it protrudes two papillae with 

 glandular hairs on its eleventh segment, and a scent is 

 exhaled which the ants like. If the ants touch with their 

 antennae a glandular area on the tenth segment, a minute 

 drop of secretion is exuded from a pair of slits, and this is 

 eagerly licked off. The secretory structures are transformed 

 glandular hairs, and they can be brought into activity by 

 titillation or otherwise. Ehrhardt induced by electrical 

 stimulation ten secretions in a minute and a half. The 

 caterpillars always have ants about them, and these are 

 doubtless of protective value. 



THE EXTRAORDINARY CASE OF PLATA —In 1896 

 Professor J. W. Gregory described and figured a Homo- 

 pterous insect, known as " Plata," or " Phromnia," many 

 specimens of which had formed on the upper part of a stem 

 an extraordinary cluster, like a flowering spike. The 

 species occurs in two forms, green and reddish, and Pro- 

 fessor Gregory's figure showed the green individuals on 

 the upper part of the stem, and the red ones beneath them, 

 the appearance being curiously like a red-flowered spike, 

 \vith green unopened buds above. In 1902 Mr. S. L. Hinde 

 pointed out that, although he had often seen Flata and its 

 larva in British East Africa, he had never seen the grouping 

 described by Gregory. He noted, however, that the red 

 and green insects in a mixed group were very like the 

 flowers and buds of a leguminous plant. Professor Poulton 

 suggested that the first specimens of a group to emerge 

 may be red, and those that issue later, green, and that Pro- 

 fessor Gregory may have seen undisturbed groups, and Mr. 

 Hinde groups which had broken up and reassembled. Each 

 of the descriptions has been subsequently confirmed from 

 tropical Africa. 



Dr. A. D. Imms, Reader in Entomology in the University of 

 Manchester, relates the lii story of the observation, and adds 

 his own very interesting experience. While touring in the 

 Himalayan foot-hills, he came across examples of an Indian 

 species, Phromnia marginella. The clusters of larvae looked 

 like groups of small white blossoms. They were covered 

 with long white waxy filaments, probably distasteful to 

 birds. The adults were found in two colours — pea-green and 

 pinkish buff — but they occurred intermixed. Out of seven 

 colonies observed, all were disposed along the middle or 

 base of branches among the fohage, and not at the apices of 

 twigs, but they were like opening buds. The white filaments 



