September 15, 1923] 



NATURE 



405 



at Zurich, and is one of a series on the morphology 

 \ of the female reproductive organs in mammals. We 

 ! understand that the histological changes in the corpus 

 \ luteum are to be dealt with later. 



! Origin and Evolution of the Elephants. — In 



' La Nature for August, Deperet and Mayet give a 

 summary of their views upon the evolution of the 

 mammoths and elephants from the Pliocene times 

 to the present day. The basis of this summary has 

 already appeared this year in an important joint 

 paper by MM. Deperet, Mayet, and Roman published 

 in the annals of the University of Lyons. This paper, 

 which deals with Elephas planifrons and the Pliocene 

 ' elephants of Europe and North Africa generally, is 

 fully illustrated in the excellent manner usual to the 

 publications of the University. The authors make 

 a step forward in the division of the genus Elephas, 

 which they now separate into eight phyletic lines 

 which themselves fall into five groups, i.e. those 

 typified by E. meridionalis, E. antiquus, and E. 

 primigenius (the mammoth) , all of which lines became 

 extinct by the end of the quaternary period ; and by 

 the living forms E. indicus, a line which is descended 

 from E. namadicus, and finally, E. africanus, a line of 

 unknown ancestry. The authors agree in large 

 measure with Osborn's view that the group is poly- 

 phyletic, but, while cutting out the genus Stegodon 

 from any close connexion with the African elephant, go 

 further than Osborn in the subdivision of the others. 



Early Pal^-ozoic Plants in Australia. — Recent 

 exploration in the mountains along the Walhalla line, 

 in Gippsland, Victoria, shows that the earliest flora 

 of a definite structural type, largely representing the 

 Procormophyta, is well developed in rocks that appear 

 to range from Upper Silurian to Upper Devonian. 

 The Silurian graptolite, Monograptus, occurs in some 

 of these beds, while in others the association of the 

 molluscs Panenka and Styliola with the plants seems 

 to suggest that the bulk of the series is Devonian. 

 Thursophyton and Haliserites (Psilophyton) are 

 typical components of this flora. Both the flora and 

 fauna of these interesting beds are now being worked 

 out by a graduate of the University of Melbourne in 

 conjunction with Mr. F. Chapman, the palaeontologist 

 of the National Museum. A detailed comparison with 

 the Rhynie flora should throw much light on the 

 early history of the vegetable kingdom. 



Defects in Colour Photographs. — It is well 

 known that in the photographic reproduction of 

 colours there are certain defects which can only be 

 eliminated by fine etching, that is, re-etching certain 

 parts of the three plates, as shown to be necessary 

 to the skilled workman. These outstanding defects 

 of the three-colour process have been fully investigated 

 by Mr. A. J. Bull, and his results are described in the 

 current number of the Journal of the Royal Photo- 

 graphic Society. His method was to measure the 

 spectra of certain colours and compare their curves 

 with those of the same colours as reproduced. The 

 errors are due to the inks used, and are summarised 

 as follows : — Blues and greens become darker and 

 greyer. Blue-greens lose their greenish hue. Pinks 

 acquire a yellow hue. Mauves become brown. Reds 

 lose any bluish tint that they may possess. Yellows 

 are lightened without change of hue, but oranges and 

 browns are well reproduced. There is a tendency 

 for the middle tones of a black to white scale to 

 become reddish. The lightening of yellows is due 

 to the yellow ink being very light. The inks are 

 transparent enough to allow of the approximate 

 calculation of the visual effect of their superposition. 

 There seems to be little immediate hope of getting 



inting inks of the theoretically correct character. 



NO. 281 I , VOL. I 12] 



Positive Rays and the Polar Aurora. — In the 

 Physikalische Zeitschrift of July i, Herr H. Bongards 

 reviews some of the available evidence as to the 

 nature of the aurora, and is inclined to favour the 

 view that it is caused by highly-charged, positive 

 argon particles, sent out with very high velocity from 

 the sun. The well-known green line, which appears 

 to be identical with that discovered by Wiechert in 

 the night sky of middle latitudes, has a wave length 

 which agrees, within the limits of observational error, 

 with a bright line in the blue spectrum of argon, and 

 can scarcely be the same as a faint line in the multiple- 

 lined hydrogen spectrum. There are also two bright 

 lines in the spectrum of the red portions of the aurora, 

 the wave lengths of which were determined with fair 

 accuracy by Vogel in 1871 ; they agree with those 

 of two lines in the red spectrum of argon ; and, while 

 further investigation is desirable, the evidence that 

 argon is concerned in the polar aurora seems worthy 

 of consideration. Bongards does not consider it 

 impossible that argon exists in the air at the height 

 of the aurora ; and suggests that it may possibly be 

 carried up by volcanic eruptions. He, however, leans 

 strongly to the view that argon particles (possibly 

 nuclei without external electrons) are ejected by the 

 sun with very high velocities, which enable them to 

 penetrate deep into the earth's atmosphere. Since 

 they have none of the electrons concerned in radia- 

 tion, they cannot emit light until, by repeated collision 

 with air molecules, they have lost sufficient velocity 

 to enable them to pick up the necessary electrons ; 

 this does not occur until the velocity is so low that 

 the Doppler effect, which appears to be small in 

 monatomic gases, cannot be noticed. 



Cellulose Acetate. — The Chemical Trade Journal 

 for August 10 contains an article on cellulose acetate, 

 a material which was first prepared by Schutzen- 

 berger in 1865, but remained a curiosity until Cross 

 (1894) obtained it by the action of acetyl chloride and 

 zinc acetate on cellulose. Cellulose acetate is the 

 basis of aeroplane " dope " (it renders taut the 

 fabric on the wings), lacquers, non-flaming celluloid 

 materials, etc. These applications are described 

 fully in the article, together with the more recent 

 processes of manufacture and the important question 

 of suitable solvents for the acetate. 



The Paths of Electrons in Solution. — A paper 

 on this subject, by L. Pisarjevski and M. Rosenberg, 

 appears in the Jour. Russ. Phys.-Chem. Soc. (1923, 54, 

 533-547). When potassium iodide solutions are 

 electrolysed, using spark electrodes, potassium hy- 

 droxide and iodine are liberated at each electrode. 

 If starch paste be added to such solutions, a blue 

 streak appears at the passage of each spark, which 

 may go vertically through the solution for a distance 

 of 9 cm., if a commutator be used, and then spreads 

 out. The addition of phenolphthalein to the solutions 

 produces a red streak under these conditions, which 

 follows a more zig-zag path than the blue one, and also 

 spreads out at its greatest depth, the coloration in 

 both cases disappearing in about 30 seconds. These 

 streaks may be deviated by applying a magnetic 

 field to the solutions. The above phenomenon is 

 explained as being due to the passage of high velocity 

 electrons from the electrodes into the solutions ; the 

 concussion of these electrons with iodine ions liberates 

 further electrons which again collide with ions in 

 solution, and leave the iodine as free atoms. The 

 free electrons also combine with potassium ions, 

 neutralising their positive charges, and producing 

 free potassium. It is thus possible visually to 

 demonstrate that processes of oxidation involve the 

 loss of electrons, and the reverse. 



