NA TURE 



[Nov. 6, 1884 



resulting from the melting by the sun of the snow above had 

 percolated down to the hard substratum, along which it had run 

 till it reached the place where the bare earth above it no longer 

 protected it from radiation, and it then cooled and crystallised 

 in this curious way, pushing itself up by. expansion in so doing, 

 each layer being the work of one night's frost. If this is 

 correct, it is not difficult to understand what I assume to be the 

 comparative rarity of this form of ice, since it would be seldom 

 that all the necessary conditions would co-exist. 



May I add, as the result of seven seasons' experience, that no 

 one who has not tried it knows the charm of Switzerland in 

 October. It is too late, of course, for high ascents, and the 

 flowers are nearly gone ; but an ordinary visitor, so long as he 

 avoids the mists and clouds of the lowlands, by keeping at an 

 elevation of three thousand feet and upwards, will find that the 

 brightness and crispness of the air, the enjoyableness of the sun- 

 shine (which in August can at best be tolerated), the purity of 

 the fresh snow, giving grandeur and beauty to lower heights 

 which in summer are mere barren rocks, and the glory of the 

 autumn colouring, not to mention the freedom from the plagues 

 of heat, flies, and tourists, render October in Switzerland the 

 most enjoyable month of the year. B. Woodd Smith 



Hampstead, October 31 



The Blackness of Tropical Man 



A decisive paper on the subject would have to be prepared 

 elsewhere, but Hindostan presents an excellent field for amass- 

 ing information with regard to the effects of an extraordinarily 

 powerful sun on the human frame's exterior. In a very interest- 

 ing article in Nature for August 21 last (p. 401), " Why Tro- 

 pical Man is Black," the cause is set down to the nerves of 

 the skin being one and all highly sensitive to light, the optic 

 nerves being merely some of those of the epidermis highly 

 specialised by long-inherited modification, and the necessity for 

 placing over them a pigment which will absorb light. Other- 

 wise the intense nerve vibrations from a light of double degree 

 power would soon degrade the tissues of the individual and 

 exhaust his vitality. 



It would have been all the better if a little more had been 

 said about the way in which a patch of dark pigment cells round 

 the transparent skin of the nerve endings, to be exalted into a 

 special sense, heighten the rates of vibration ; or how the 

 selected tissue, at the same time securing the transmission of 

 heat, as the constant accumulation of heat waves behind it, 

 throws the molecular constituents of the protoplasm "into the 

 highest rates of vibration possibly obtainable with the means at 

 disposal.'' 



Before turning to the cupciience India affords, it has to be 

 noclced that, taking the centre of Europe as the standard of 

 whiteness, it is not only going south that the population becomes 

 successively blacker, but that there is a dark-skinned tendency 

 in the races lying in the other direction, towards the Polar re- 

 gions. Besides this, exposure in the bright days of August on 

 the moors in the British Isles has the effect of browning the 

 white skin exposed to light, and making it on the face and hands 

 for a short time only a shade lighter than the lightest Indians. 

 This can only be by the solar rays producing pigment in the 

 skin. 



On the contrary, the experience of Europeans in India is that 

 the sun there does not burn ; if anything, it rather whitens them 

 and pales the complexion. It is only on certain occasions, when 

 the sun is obscured by rain-clouds, it is cool, and the diffused 

 light is of a particular but unascertained actinic quality, that the 

 skin of a European is sunburnt. One may ride all day in the 

 hottest sun and have no trace of sunburning. 



Also were light the sole cause of a protection for the skin 

 being required, this would be supplied by the clothing Euro- 

 peans invariably have, except on hands and face; and they 

 would be placed in about the same favourable position as the 

 natives, if not more so, as those of the latter of the class of 

 labourers prefer working almost entirely without clothes. 



\\ hat is dreaded by Europeans all over India, and extending 

 into Afghanistan, is the "Indian sun," when it is elevated more 

 than ten or fifteen degrees above the horizon ; and it is chiefly 

 the head which it affects, and which has to be protected by 

 non-conducting materials, forming the strange head-gear of the 

 tropics. The playing of the sun on the rest of the body is 

 disagreeable, but not dangerous. 



Light and heat are one and the same, so that the nerves of 



sight are only a select number of those with which the skin is 

 full, higher strung ; but it is noticeable that, though heat is felt 

 by any nerves of the skin indiscriminately, they are insensible to 

 minute differences of heat, or in the periods of the heat-rays, 

 so that no sense, so to speak, is conveyed by them. That is — 

 though, as we know, all objects reflect as many heat-rays of 

 different kinds as they do visual rays — we are not conscious of 

 their form by a reception and discrimination of the varying 

 periods of the heat-rays ; we do not consciously see by heat. 



The effect the Indian sun has on European health, sunstroke 

 being said to be the work of a few minutes, shows that the 

 nerves of the skin are sensitive to some rays besides those of 

 light. In fact, the sun's rays of Hindostan must contain rays 

 not found in the sunlight of most other parts of the world, which 

 moreover penetrate the European's white skin tissues and 

 clothing, while the natives can let it beat upon their bared heads 

 with complete impunity. 



There has never been a sufficiently minute comparison made 

 between the pure solar diffraction spectrum, from the lowest 

 lines to the highest, of India and that in other countries, such as 

 Great Britain, America, the We-t Indies, and Australia. In 

 many respects the West India Islands are as tropical as the 

 East Indies, but those who have resided in the former and 

 coming to the latter declare there is some quality they feel in the 

 Indian sun that is absent in the West Indies ; they can wear a 

 simple straw hat in the one place, but could not attempt it any- 

 where throughout India. II the spectra were juxtaposed, it 

 would no doubt be found that groups of rays in some portion of 

 it, whether at the red or the violet end, were present to much 

 larger extent in the light of the Indian sun than either in Aus- 

 tralia or the West Indies. It is of the greatest importance, in 

 order to clear up this question, as well as to science in general, 

 that those who have the means and time should analyse the 

 spectra and give the results. 



The only test available is sensation at present, but this is 

 unmistakable, because, in addition to the burning feel of 140 

 Fahrenheit, there is a peculiarly unpleasant sensation even in 

 the shade, whether it is that of a tree, an umbrella, a thin tent, 

 or even a walled room with a window, if there is no veranda. 

 This can only come from invisible rays to which all but the 

 thickest coverings are pervious, and which the skin and tissues 

 admit freely. 



European "colonists " are, happily for themselves, unknown 

 in India, and the race would immediately die out, as it is only 

 by frequent visits to temperate climates that a European can 

 preserve health. But if they did exist it is open to doubt if a 

 white skin would ever become black. It is commonly supposed 

 that the Black Jins of Cochin are converted Hindoos. The 

 difference that a change in dress and diet makes in these is 

 singular, many being termed Portuguese, for example, who are 

 pure natives descended from converts whom the Portuguese for 

 the most part made forcibly. 



As a rule, the higher the caste andthehigher in the scale a native 

 of India is, the whiter he is ; and the lower the caste and hotter 

 the mean temperature of the place, the blacker. But this is not 

 invariably the case, as the outcasts who work in leather in Upper 

 India are rather lighter than some of the Brahmans. However, 

 latitude has m >st effect, and wherever the sun is hottest all the 

 year round the blacker the natives, down to the equator of heat 

 shown on the atlases. The configuration of the country, how- 

 ever, shows that the shades of colour are due to successive waves 

 of conquest from the north, and the Northern Asiatics, who 

 were nearly white at first, degenerate the farther south they 

 come, and are unfit for labour. A blackness of skin, therefore, 

 confers an immunity from the effects of the sun, so that those 

 having it can labour in the heat in a way that would soon cause 

 the lighter races to give in. 



Black radiates quicker than white, and though black coats are 

 by no means unknown to Europeans in India, who are as often 

 in those as in coats of any other colour, the black skin of the 

 labourer would throw off" accumulated heat much more quickly 

 than if white, and perhaps in a ratio worth calculating. This 

 must be one of the reasons; and it may be noticed that the 

 exterior of buildings is frequently tinted a slate colour with this 

 view, in India, instead of being whitewashed. 



Still a more ready dissipation of heat is not the only advan- 

 tage imparted by a pigmentary blackness in the human skin ; 

 and it is to be inferred that the real protection consists in there 

 being a few of the invisible solar rays of the spectrum in tropi- 

 cal light injurious to man, which nevertheless possess unusual 



