May 31, 1888] 



NATURE 



ior 



The Land of the Pink Pearl. By L. D. Powles. (London : 

 Sampson Low, 1888.) 



Mr. Powles served for some time as a circuit justice in 

 the Bahama Islands, and in the present volume he com- 

 municates the impressions produced upon him both by 

 the islands themselves and by their inhabitants. He 

 makes no profession of an intimate knowledge of any 

 branch of science, so that the work contains few elements 

 of interest that call here for special notice. We may 

 say, however, that the book is written in a lively and 

 agreeable style, and that the author has brought together 

 much useful general information about what he calls 

 <l this obscure corner of Her Majesty's dominions." The 

 most valuable passages are those in which he deals with 

 the relations between the white and the coloured popula- 

 tion. His statements on this subject are certainly not 

 lacking in vigour, for he speaks of the African race in 

 the Bahamas as being "ground down and oppressed in a 

 manner which is a disgrace to British rule." When Mr. 

 Powles went to the Bahamas, he had an impression that 

 negroes were "intended by Nature to be kept in subjec- 

 tion by the whites." Experience, however, led him to 

 modify this extravagant notion. Referring to the state- 

 ment, so often made, that "it is impossible to produce 

 anything by free negro labour," he sensibly suggests that 

 " perhaps if the Imperial Government would establish an 

 agricultural college and give the coloured race in the 

 Bahamas a fair chance, we might see a different state of 

 things." The physical deterioration of the coloured 

 people is, he thinks, sufficiently accounted for by their 

 wretched food and by the unhealthy nature of the places 

 in which they are compelled to live. Curiously enough, 

 Africans in the Bahamas retain their original tribal 

 distinctions ; and Mr. Powles says that every August 

 some tribes elect a queen whose will on certain matters 

 is accepted as law. 



A Treatise on Alcohol, with Tables of Spirit- Gravities. 

 By Thomas Stevenson, M.D. Second Edition. (Lon- 

 don : Gurney and Jackson, 1888.) 



The present edition of this useful little work, originally 

 published under the title of "Spirit-Gravities," contains 

 a critical account of the various determinations of the 

 specific gravity of alcohol, and introduces the most recent 

 investigations— those of Messrs. Squibb— on this subject. 

 These investigations do not, however, affect the accuracy 

 of the alcoholometric tables, which are therefore reprinted 

 unchanged. 



LETTERS TO THE ED L TOR. 

 [The Editor does not hold himself responsible for opinions 

 expressed by his correspondents. Neither can he under- 

 take to return, or to correspond with the writers of, 

 rejected manuscripts intended for this or any other part 

 of Nature. No notice is taken of anonymous communi- 

 cations.'] 



The Dispersal of Seeds by Birds. 



It should be borne in mind by readers of Nature in various 

 parts of the world that many facts bearing on this matter may be 

 collected with very little trouble. At Mr. Thiselton Dyer's 

 suggestion I take this opportunity of supplementing my letter to 

 Mr. Botting Hemsley (Nature, vol. xxxviii. p. 40). 



The frigate-birds, petrels, gannets, boobies, &c, that frequent 

 in numbers the guano islands of the Pacific, will present oppor- 

 tunities of investigating this subject rarely found elsewhere. Not 

 only the crops, but also the feathers and feet should be examined, 

 since seeds have been sometimes found adhering to sea-birds that 

 have been sitting on broken eggs. The industries connected 

 with the ocean- ranging mutton-bird in Ba?s's Straits, and with 

 the grebe in South America, may afford other opportunities. 

 The seal-fisher in the Southern Ocean, and the sportsman on 

 some remote coral islet, the voyager around the Cape, and the 



lighthouse-keeper in southern climes, these and many others 

 might take a practical interest in this subject. It is important 

 that not only should the seeds and fruits be preserved and sent 

 to Kew, but that the species of bird should be known ; and for 

 this purpose, where there is any doubt, the wing or head of the 

 bird might be also .'ent. H. B. Guppy. 



May 27. 



Nose-Blackening as Preventive of Snow-Blindness. 



As a partial answer to Prof. Ray Lankester's inquiry on 

 nose-blackening as preventive of snow-blindness, may I offer 

 some observations which I have made in my many wanderings in 

 the higher Alps in early summer, when I have necessarily had 

 much experience of the effects of snow on the human body ? 



But first I should like to draw attention to a letter of the Hon. 

 Ralph Abercromby in Nature (vol. xxxiii. p. 559), which he was 

 kind enoug h to send me, relating some experiences on nose and 

 face blackening in Morocco to prevent sand glare, in Fiji to 

 prevent water glare, and in Sikkim to prevent snow glare. It 

 was very curious that the Fijians, who ordinarily painted their 

 faces white and red for ornament, would, before going fishing on 

 the reefs in the full glare of -the sun, blacken them. Mr. Aber- 

 cromby draws attention very naturally to " the strange anomaly of 

 physiological experience apparently contradicting the teachings of 

 pure physics. Charcoal black, which is used in physical experi- 

 ments as the best absorbent of every kind of heat radiation, is 

 practically used by three races at least, to protect one of the most 

 sensitive human organs from reflected light and heat." 



Experience has, I think, sufficiently shown that snow-blindness 

 and snow-burn, or sunburn on snow, own the same causes for 

 their production ; and, as nowadays both guides and climbers in 

 the Alps invariably take the precaution of protecting their eyes 

 with coloured spectacles, snow- blindness is rarely heard of. 

 My observations are almost entirely confined to the causes of 

 sunburn. 



It will, I think, be readily conceded by Alpine climbers that 

 sun on the snow burns more quickly than on rocks or in the heated 

 valleys at a lower elevation. This increased power of burning 

 appears somewhat singular when one reflects that the heat rays 

 must be occupied in the melting of the snow, and thus rendered 

 latent. 



Iron-workers, glass-workers, and others are constantly exposed 

 to a heat of 400 or 500 F., and yet do not become burnt ; and 

 there can be little doubt that the enormous radiation from heated 

 rocks and valleys, in addition to the direct rays of the sun, make 

 up an amount of heat far greater than is ever experienced on even 

 a very sunny snow slope, and yet one does not become sunburnt. 

 No doubt the surface of the snow reflects and disperses much 

 heat, but certainly far less than it receives, as heat rays are ab- 

 sorbed and rendered latent by the snow-melting and evaporation. 

 Experience fully corroborates this, for one may often lie on one's 

 back and freely expose the face for long periods to the sun and 

 yet remain unburnt. There must therefore be some other factor 

 in sunburn than heat alone. 



In discussing the subject with Prof. Tyndall, he added the 

 very interesting and significant fact that he was never more burnt 

 en snow than whilst experimenting with the electric light at the 

 North Foreland Lighthouse, where there was no heat sufficient 

 to produce such an effect. 



I am aware that sometimes, in peculiar conditions of the atmo- 

 sphere, the direct sun's rays will burn. I have met with some 

 singular instances where several persons have been burnt on the 

 same day, even in England, who had never previously suffered in 

 that way. I am further aware that sometimes (not always) in a 

 dead calm on a ship's deck one may be severely burnt, and that 

 in boating on a river the same may occasionally happen. Masks 

 and veils have been long used as a protection on snow, and are 

 more or less successful ; brown veils and glasses in my experience 

 being the most efficient. As bearing upon this, I may mention 

 that a friend of mine after an ascent on snow had an enormously 

 swollen face, and I observed that in the general swelling there 

 were many pits or depressions, and that each pit corresponded to 

 a freckle : the irritating rays had been intercepted by the brown 

 colour of the freckle. About the same time, I encountered a 

 paragraph in the Lancet, saying that a German savant had been 

 experimenting on the effects of sunlight on the retina, and had 

 found that it had destroyed the visual purple of the retina, but 

 that the action was modified by transmitting the sun's rays through 

 various coloured glasses, and that when transmitted through 



