August 8, 1901 



NA TURE 



oO' 



LETTERS TO THE EDITOR. 

 [ Thi Editor does not hold himself responsible for opinions ex- 

 pressed by his correspondents. Neither can he undertake 

 to return^ or to co} respond with the writers of rcjer.el 

 :iiantiscripis intended for this or any other part of Nature. 

 No notice is taken of anonvmous communications.'^ 



Hair on the Digits of Man. 



The distribution of hair on the dorsal surfacei of the digits in 

 man, anthropoid apes and monkeys, is referred to by Romanes 

 in " Darwin and alter Darwin,"' but its significance seems to be 

 overlooked. I would venture to suggest that these facts bear a 

 Lamarckian, and only a Lamarckian, interpretalion. It is clear 

 that if acquired characters can be inherited through use, habit 

 or environment, the loss of certain characters through habit and 

 the like may also be inherited, and the development of characters 

 on the one hand and the decay of characters on the other will 

 be sufficient to prove that Weismann's great rule is not absolute. 

 Use-inheritance and disuse-inheritance ought both to be capable 

 of proof. It may be difficult, or impossible, to prore the greater 

 cases, such as the long cervical vertebrae of the giraffe and the 

 great horns of the elk, and indeed most of the instances brought 

 forward by Herbert Spencer, Eimer and Cunningham. These 

 may lie open to a selectionist interpretation. But it becoines 

 well-nigh impossible to carry such aa interpretation into the 

 trifling biological characters to which I would briefly refer. 



In man, hair is entirely wanting on the ungual phalanges 

 of his hand and foot, very rare on the middle phalanges of either 

 foot or hand, and always present more or less on the first row 

 of phalanges in both foot and hand. On the middle phalanges, 

 where it occasionally occurs, it is best looked tor in early child- 

 hood, when the hair is more strongly developed than in infancy, 

 and when it has not yet disappeared through secondary causes. 

 I have just examined the case of a child of four and a half years 

 old with marked hair on the middle phalanges of the four digits 

 on the hand, and on the second, third and fourth digits of the 

 foot, and with none on the fifth digit, except on the first phalanx. 

 It is worthy of remark here that many of the facts of hair- 

 direction, being somewhat fugitive in character, are best studied 

 in the human subject in childhood. 



Assuming that man is the child of the monkey, it follows 

 that his ancestors possessed at one time hair on all the phalanges 

 of both foot and hand, as is the case in all the existing monkeys 

 of the Old World and New World that I have been able to ex- 

 amine ; though a Chacma baboon at the London Zoological 

 Gardens shows abundant hair on all the phalanges of the foot, 

 and on the middle and ungual phalanges of the hand either 

 no hair or the small amount that is present very much worn 

 down. In the few anthropoid apes that I have been able to 

 examine, the chimpanzee resembles the human subject in this 

 character, and the young orang at the Zoological Gardens 

 possesses hair like that of the lower monkeys, i.e. on all the 

 phalanges of foot and hand, though on the two terminal 

 phalanges of the hand the hair is worn down and quite bristly, 

 even though the animal is still young. 



Broadly speaking, these facts are congenital and must be 

 acquired, either through heredity, variation and selection, or 

 as the result of habit, such as that of friction, acting through 

 numerous ancestors in a similar direction. We need only bear 

 in mind how much greater is the exposure to friction, in the 

 movements of the hand of man, of the ungual and middle 

 phalanges than that of the first phalanx to see that the con- 

 clusion as to the Lamarckian view here put forward is difficult 

 to resist. 



This very small point seems to be more worth considering 

 than its intrinsic importance would warrant, in consequence of 

 the way in which a disputed biological doctrine, such as that of 

 Weismann, is being exploited in a somewhat serious matter. It 

 is enough to quott, W. K. Brooks, of America, and Prof. J- 

 Arthur Thomson, of -Aberdeen, in support of the statement that 

 Weismann's doctrine is " not proven." I refer to the long and 

 somewhat heated discussion which has taken place recently in 

 the columns of the Lancet on the subject of " Legislation 

 against National Intemperance." The greater vigour of assertion 

 and multitude of words, if not greater logic, rests with the advo- 

 cates of the view that alcoholism is a selective influence of value 

 in the evolution of man and ought not to be interfered with by 

 legislation. The reasons for this startling contention are 

 numerous, but their justification rests ultimately on the doctrine 



NO. 1658, VOL. 64] 



of Weismann carried to the bitter end, viz. that acquired cha- 

 racters are not inherited. I submit that if it can be shown that 

 no other than a Lamarckian interpretation of certain small phen- 

 omena is possible, something may be done towards making a 

 breach in a somewhat dangerous citadel. WAt.TER Kidd. 



July. 



Pseudoscopic Vision without a Pseudoscope : A Newz 

 Optical Illusion. 



A METHOD oi securing an illusion of binocular vision wholly 

 without instrumental aid occurred to me recently, which is in- 

 teresting in connection with the study of pseudoscopic vision. 

 It is fully as startling as any of the results obtained with the 

 lenticular pseudoscope, which I showed at the Royal Institution 

 in February, 1900, and which I shall speak of presently, and, 

 requiring the aid of no optical instrument, is much more 

 impressive, 



A lead pencil is held point-up an inch or two in front of a 

 wire window screen, with a sky background. If the eyes are 

 converged upon the pencil point, the wire gauze becomes some- 

 what blurred, and of course doubled. Inasmuch, however, as 

 the gauze has a regularly recurring pattern, the two images can 

 be united, and with a little effort the eyes can be accommodated 

 for distinct vision of the combinfd images of the mesh. To ac- 

 commodate for a greater distance than the point upon which the 

 eyes are converged requires practice, but the trick is very much 

 easier in this case than in the case of viewing stereoscopic 

 pictures without a stereoscope. 



As soon as accommodation is secured, the mesh becomes per- 

 fectly sharp and appears to lie nearly in the plane of the pencil 

 point, which still appears single and perfectly sharp. If now 

 the pencil is moved away from the eyes which are to be kept 

 fixed on the screen, it passes through the mesh and becomes 

 doubled, the distance between the images increasing until the 

 point brings up against the screen. If now the pencil be re- 

 moved it will be found that the sharp images of the combined 

 images of the gauze persists, even though the eyes be moved 

 nearer to, or farther away from, the screen. Biing the eyes up 

 to within six or eight inches of the plane in which the mesh 

 appears to lie and attempt to touch it with the finger. It is not 

 there: the finger falls upon empty space, the screen being in 

 reality a couple of inches further off. This is by all means the 

 most startling illusion that I have ever seen, for we apparently 

 see something occupying a perfectly definite position in space 

 before our eyes, and yet if we attempt to put our finger on it we 

 find that there is nothing there. 



It is best to begin by holding the pencil an inch or less in 

 front of the screen. .-\s the eyes become accustomed to the 

 unusual accommodation, the distance can be increased. I have 

 succeeded in bringing up the apparent plane of the mesh, five or 

 six inches, but this requires as great a control over the eyes 

 as is necessary in viewing stereoscopic pictures without ai> 

 instrument. 



The pseudoscope, which I have alluded to above, I have 

 described in Science (about November, 1899), but inasmuch as 

 the description of it which I sent to N.'iTURE, the editor informs 

 me, was never received, a brief account of it may not be out of 

 place. Two lenses of about three inches focus are mounted in 

 front of a pair of stereoscope lenses in such a way that the real 

 inverted images formed by them in space can be combined by 

 the stereoscope. The lenses should be mounted in slide tubes 

 attached to the frame of the stereoscope, so that proper focussing 

 can be accomplished. This instrument has been named the 

 lenticular pseudoscope by the psychologists, and gives results far 

 superior to those obtained by the Wheatstone and other forms 

 of mirror pseudoscopes. Viewed through the instrument, a 

 hollow bowl appears as a beautifully convex dome, and if a 

 marble be dropped into it we witness the astounding 

 phenomenon of a ball rolling up hill, crossing the top, des- 

 cending part way down the other side and then returning to the 

 summit, in defiance of the law of gravitation. 



Johns Hopkins University. R. W. Wood. 



Markings on Jupiter. 

 There is a large, dark spot on the southern side of the 

 S. equatorial belt (and nearly in same latitude as the red spot) 

 which on July 24 was preceded by a number of small black dots 

 5° to 10° apart, according to the observations of Dr. Kibbler, of 

 Stamford Hill, who appears to have been the first, or one of the 



