December 13, 1900] 



NATURE 



157 



several hundred feet, using the form of coherer described, and, 

 therefore, I am unable to compare its sensibility with that of the 

 usual form. 



Undoubtedly it would prove to be less sensitive, but for use 

 over a moderate distance it forms a convenient instrument for 

 the purpose of demonstration. Augustus Trowbridge. 



University of Wisconsin, U.S.A. 



Secondary Sexual Characters and the Coloration of the 

 Prong-buck. 



The weak spot in Mr. Cunningham's argument (Nature, 

 November 8, p. 29) lies in his believing it to be conceded that 

 secondary sexual characters which are the outcome of male kata- 

 bolism need no explanation by the theory of sexual or of natural 

 selection. Starting with this assumption, he points out that, 

 since these characters are often not developed, male katabolism 

 does not exist in such cases, or exists without producing any 

 visible effects. He therefore rejects male katabolism as^ the 

 cause of the variations and introduces in its stead " nervous' and 

 muscular activity " and " the habits of life and external condi- 

 tions. 



Whether Mr. Cunningham's hypothesis is an improvement 

 upon that of Geddes and Thomson or Wallace may be doubted ; 

 and, so far as his views are intelligible to me from the brief 

 epitome his letter contains, they labour under the disadvantage 

 of involving an acceptance in the Lamarckian doctrine and the 

 transmission of acquired characters — problems which, seductive 

 and important though they be, are as yet insufficiently supported 

 by evidence and, whether true or false, stand aside from the 

 Darwinian theory, neither refuting nor confirming it. 



After all, " male katabolism," " metabolism " and '* physio- 

 logical activities " are in this connection merely names assigned 

 to the unknown primary cause of certain male characters, and, as 

 such, are nothing but imposing substitutes for the ' ' vital force " 

 of the pseudoscientific realists. 



Setting on one side the question of the initial cause of 

 variation, I am quite unable to agree with Mr. Cunningham 

 that secondary sexual characters may reach a high standard 

 of perfection and be maintained in a state of stability by 

 "physiological processes" without the controlling influences 

 involved in the struggle for existence. Sexual variations, once 

 started, must fall, like other variations, under the influence of 

 external conditions ; those which are harmful will be eliminated ; 

 those which are beneficial selected and preserved. Therefore, con- 

 sidering the diversity of the conditions under which species live, 

 the needs that have to be satisfied, the enemies that have to be 

 avoided, it is no matter for surprise that, even in the males of 

 closely allied forms, the sexual characters vary in degree of 

 manifestation, are sometimes suppressed, sometimes developed ; 

 or, taking the particular case Mr. Cunningham mentions, that 

 the nigrescence of the bull kudu and nilghaie may, as I have 

 suggested, be checked for purposes of concealment in the one 

 and emphasised as an ornament or advertisement in the other. 



One or two points in Mr. Cockerell's criticism of a footnote 

 (Nature, October 15, p. 58) call for comment. His suggestion 

 that Mr. Wallace cites the prong-buck as an instance of recog- 

 nition-marks in the sense* in which these terms were employed 

 in my article is inexact ; and his opinion that I completely 

 overlooked the point of a theory I was not discussing is, I 

 can assure him, erroneous. Moreover, in spite of his incredulity, 

 I venture to repeat that the prong-buck, with its white belly 

 and darker upper side, is an illustration of Thayer's principle. 

 That its patterns are to be explained exclusively on this principle 

 I did not assert. With regard to Mr. Cockerell's reasons for 

 rejecting the view that the prong-buck is procryptically coloured, 

 I would commend the following facts to his consideration. 

 Zebras and giraffes can be " seen from afar off in herds," they 

 seek " safety in flight," and they have the same " necessity for 

 keeping together when in flight " that the prong-bucks have. 

 Nevertheless, these animals are known to be procryptically 

 coloured, though the fact is by no means always evident to 

 those who " have had the pleasure of seeing them in their 

 native wilds." R, I. POCOCK. 



November 18. 



A New Race of Musk-Qx. 



Mr. Rowland Ward has on view at his establishment in 

 Piccadilly a mounted adult male and female musk-ox from East 

 Greenland, which differ from the ordinary form in having a large 



NO. 1624, VOL. 63] 



whitish patch on the face, as well as in certain other details of 

 coloration. They may be made the types of a new race, under 

 the name Ovibos moschatus wardi. The female was recently 

 exhibited at the Zoological Society. R. Lydekker. 



Harpenden, December 10. 



The Optics of Acuteness of Sight. 

 In reference to the letter of Mr. Percival in your issue of 

 November 22 (p. 82), concerning acuteness of vision, it is 

 interesting to determine the power of resolution of the eye con- 

 sidered as a lens merely, according to the well-known rule, 



fl=_x2'44. 



A 



Where Q is the angular diameter subtended at the second 

 nodal point by the first dark ring of the diffraction image of a 

 distant point, A is the aperture of the lens, and X is the wave- 

 length of the radiations (supposed homogeneous) from the dis- 

 tant point. 



Taking A for the eye as 4 mm., and A. as 0*000589 mm. 

 (yellow light) the value fl = i '2' is obtained. 



Hence the diffraction image of a luminous point on the retina 

 may be taken as rather less than i' in angular diameter (the 

 brightness of the diffraction disc rapidly decreasing towards the 

 first dark ring). 



It would thus seem that, should any considerable superiority 

 of acuteness of vision exist among savages the cause should be 

 looked for in the aperture of the iris, as well as in greater 

 detail of the retina. F. Twyman. 



54, Haverstock Hill, London, N.W., November 26. 



Euclid i. 32 Corr. 



With reference to Mr. Allman's letter in Nature of 

 November 29, the following will, I think, be of interest. 



In Proclus' (411-485 A.D.) commentary printed at the end 

 of the Editio Princeps of Euclid (Grynaeus-Bale, 1533 a.d.) 

 these two corollaries are given : — 



( 1 ) The sum of the interior angles of any polygon is equal to 

 twice as many right angles as the polygon has sides less two. 



(2) The sum of the exterior angles of any polygon is equal to 

 four right angles. Stam. Eumorfopoulos. 



33, Gloucester Square, Hyde Park, W., December 3. 



A PLEA FOR THE STUDY OF THE NATIVE 

 RACES IN SOUTH AFRICA. 



T N a recently-published work Dr. P. Topinard makes the 

 ^ statement that ethnography is cultivated in England 

 because it leads to a knowledge of the natives, and thus 

 prepares the means of turning them to account. This dis- 

 tinguished French anthropologist appears to have per- 

 mitted his dispassionate judgment to have temporarily 

 forsaken him. Alas ! ethnography is but little cultivated 

 in this country, and it may be said to be almost entirely 

 neglected by our Government. It was to take away 

 this reproach in some measure, and to seize the present 

 opportunity in South Africa, that led Mr. E. Sidney 

 Hartland, the President of the Folklore Society, to read 

 before the Anthropological Section of the British Associa- 

 tion at Bradford a very carefully considered and tem- 

 perate paper, " On the Imperfection of our Knowledge of 

 the Black Races of the Transvaal and Orange River 

 Colonies." 



Mr. Hartland stated that on the pacification of these 

 colonies one of the first problems confronting us would 

 be the management of the native black population. 

 This led to the question, What did we know of the 

 African races of these provinces ? It must be confessed 

 that we knew very little. Our hunters had hunted big 

 game through the land ; our missionaries had taught the 

 natives ; our traders had traded with black and white ; 

 our soldiers had fought in the country, and during the 

 last twenty years mining adventurers had exploited the 

 mineral products. None of these, except the mission- 

 aries, had had any real interest in the natives ; conse- 

 quently, few of the others had recorded anything of value 



