December, 1906.] 



KNOWLEDGE & SCIENTIFIC NEWS. 



617 



eye. Lines drawn from the extremities of this image 

 through the second nodal point of the eye till they meet 

 the retina mark out very nearly, indeed, the retinal area 

 affected. This area is found to sensibly coincide with the 

 area of the yellow spot, whose diameter is from 8 mm. to 

 I mm. The fovea central^ is only .2 mm. diameter. Hence 

 Brewster and Helmholtz were wrong in attributing this 

 effect to the centre region alone. Throughout the yellow 

 spot the retinal rods are absent, only cones being present ; 

 and it would seem as if a close connection existed between 

 this peculiar retinal structure and the detection of polarised 

 light" and the plane of polarisation by the unaided eye. 



Haidinger, a mineralogist, geologist, and physicist of 

 considerable note, was born at Vienna in 179s, and died in 

 1871. In 1S22 he took up his abode for a time in Edin- 

 burgh, after which he returned to Vienna. On the com- 

 pletion of the Geological Survey of the Austrian Dominions 

 in 1862, he superintended the preparation of the maps which 

 were issued. 



Alpha Particles. 



Professor Rutherford has completed an investigation 

 along with Dr. O. Hahn which shows that, from whatever 

 radio-active source alpha particles arc obtained, their pro- 

 perties are identical. This statement applies not only to 

 the particles from the various products of radium, but also 

 to those from actinium and thorium. The observed value of 

 the charge per unit mass comes out about 5,000. The 

 corresponding value for hydrogen as measured in electro- 

 lysis is nearly 10,000. The hydrogen ion is supposed to be 

 the hydrogen atom with a positive charge ; so that (taking 

 the mass of an atom of hydrogen as unity) the above num- 

 ber, 10,000, represents the positive charge on an atom of 

 hydrogen. If the charge on an alpha particle is taken as 

 being the same as that on an atom of hydrogen the mass of 

 an alpha particle must be about 2. Now, there is very 

 plausible evidence that the alpha particles either consist of, 

 or are easily transformed into, helium atoms. But the 

 mass of a helium atom on the same scale is 4. If the belief 

 in the practical identity of the helium atom and alpha 

 particle is adhered to it is necessary to suppose that the 

 latter carries twice the positive charge on a hydrogen atom ; 

 or, in other words, carries the same charge as that on any 

 divalent atoms, such as the copper in cupric salts. 



Erratum. — In the Physical Notes for October, the focal 

 length of a combination of two lenses should have been 

 given as fifj/K instead of f^i/K. 



.^^^^^^ 



ZOOLOGICAL. 



By R. Lydekker. 

 The Internal Ear of Mamnnals. 



TllR method of preparing Ihc membranous labvrinth of the 

 internal ear of mammals invented by Dr. .Mberl Gray has 

 resulted in some important observations on the structure 

 of this region in various mammals, which are recorded in 

 a recent issue of the Proceedings of the Royal Society. 

 From an examination of sixteen species. Dr. Gray has been 

 enabled to state that there are differences in the form of 

 the cochlea, in the size of the perilymphatic space of the 

 semi-circular canals, and in the relative size of the otoliths. 

 Apart from its altogether peculiar modification in the egg- 

 laying group, the cochlea presents two main tvpes ; namely, 

 a sharply pointed one, characteristic of carnivores and 

 rodents, and a flattened one found in man, monkeys, 

 lemurs, ungulates, and cetaceans. The seal is, however, 

 an exception in this respect among the carnivora, the 

 cochlea being boat-shaped rather Ih.an pointed ; and among 

 the ungulates the flattened form is least develoned in the 

 pig- 



As regards the perilymphatic space of the semi-circular 

 canals, this is relatively large in man, monkeys, and the 

 seal, but in the other species examined it is either minute or 



wanting. Hitlierto the otoliths have been assumed to be 

 very small in all cases, but those of the porpoise, the seal, 

 and the kangaroo have already been proved to be exceptions 



to the rule. 



Popular Science Teaching. 



In the Museum Ga-rtte for October, occurs the following 

 sentence : — " The ichthyosaurus was a four-footed reptile 

 which had taken to the water and received modifications 

 (loss of feet, etc.), just as the whale is a four-footed mammal 

 which has taken to the water and lost its letrs." Later on 

 we read that : " In the manatee and dugong, all the digits 

 are webbed together into a fin, but upon this fin rudimen- 

 tary nails arc produced. In explanation of this W"e must 

 remember that the nails are modified parts of the skin, and 

 are not formed in connection with the bones." 



Should the writer of these passages read them again, we 

 wonder whether he would feel w-hoUy satisfied with the 

 manner in which he has expressed himself. .Xtrain, we 

 wonder whether, on reflection, he really believes another 

 statement in the same issue to the effect that the tenrec of 

 Madagascar and the European hedgehog inherit their 

 propensity to slumber from a common ancestor. 



New Antelopes. 



Africa still continues to yield something new in the way 

 of animals ; this time in the shape of a couple of antelopes 

 of more than ordinary interest, which have recently been 

 described in the columns of the Field. The first of these is 

 an eland, from British East .Africa, of which the mounted 

 head and the body-skin have been presented to the British 

 Museum by Colonel Patterson, its discoverer. The presence 

 of a white chevron on the forehead and certain other 

 details of colouring distinguish this eland (Taurotrnrius oryx 

 pattersonianus) from its kindred further south. Not much 

 in this, the reader may say. As a matter of fact, it is of 

 great importance (so far as it is justifiable to use that term 

 in connection with natural history), since a similar chevron 

 is found in the elands of the Bahr-el-Ghazal and .Senegam- 

 bia, which have been regarded as specifically distinct from 

 the southern animals. Colonel Patterson's specimens suggest 

 that all will prove to be local phases of a single species. 



The second new species, based upon a mounted head, shot 

 bv Captain P. E. Vaughan, in the south-western district 

 of the Bahi-el-Ghazal province of the Sudan, and presented 

 bv him to the British Museum, is a near relative of that 

 handsome member of the watcrbuck group from the ^^'hite 

 Nile and the .Sobat known as the white-eared kob (Cobus 

 leucotis). The old bucks of the latter are characterised 

 by the ears and much of the jaw, as well as the chin, the 

 throat, and vmder-parts being white, while the rest of the 

 upper surface is deep blackish-brown. In the new species 

 the general plan of colouring in the adult bucks is nearly 

 similar ; but the coloured area is foxy red in place of dark 

 brown. Cobus vauijliaiu, as the new species is called, is 

 therefore a connecting link between the white-cared kob and 

 the nearly uniform chestnut species found in L'ganda and 

 West .\fr'ira. 



Crocodile Leather. 



A correspondent in the trade, who is a reader of 

 " Knowi.f.dc.k," has sent mc two specimens of commercial 

 crocodile leather, with the request that I would give a note 

 upon them in this column. The one specimen is from 

 Mexico, and the other from Florida. In the former, the 

 place occupied by each scale is occupied by a small pore, 

 situated near one end ; while in the other such pores are 

 cither entirely wanting or are represented by mere traces 

 in some of the spaces. My informant states that these 

 characters are quite constant in Mexican and Florida skins 

 respectively. .Mr. G. A. Boulenger, of the British Museum, 

 tells me liiat both specimens are from the leg, and that 

 while the Mexican example is taken from the American 

 crocodile (CrocodUus amcricanus), the Florida specimen is 

 the product of the Mississippi alligator (Ailifiator 

 mississippicitsis). I am further informed that the pores are 

 connected with sensory organs, ^^'hy they should be fully 

 developed in the one species and practically obsolete in the 

 other, remains to be explained. 



