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the heated face tends to retreat with a force proportional both to the density of the gas and to the area of the surface.
A calculation of the absolute value of the excess of pressure cannot be made without further hypothesis. If we were to suppose that the molecules, after collision with the heated face, rebound with the same velocities (v+dv) as they would have were the temperature raised throughout, the pressure would be increased in the ratio v+(v+dv): 2v or 1+dv/2v: 1. On the other hand, if the temperature were actually raised throughout, the pressure, according to the usual gaseous laws, would be increased in the ratio (v+dv)2: v2 or 1+2dv/v: 1. On this hypothesis, therefore, the unbalanced increment of pressure on the heated face is one-quarter of the increment that would be caused by a general rise of temperature to the same amount. This estimate is necessarily in excess of the truth, but it is probably of the right order of magnitude.
The supposition upon which our reasoning has been based, viz. that the mean free path of a molecule is large in comparison with the linear dimension of the vessel, has been made for the sake of simplicity, and is certainly a very extreme one. It is not difficult to recognise that in the extreme form it may be dispensed with. All that is really necessary to justify our conclusions is that the mean free path should be very large in comparison with the vane. The magnitude and distribution of the velocities with which the molecules impinge will then be independent of the fact that the face of the vane is heated, and this is all that the argument requires. The repulsion by heat of a silk fibre suspended in a moderately rare gas was, it will be remembered, verified by O. Reynolds. RAYLEIGH.
LIFE IN AN OASIS.1
ALTHOUGH the oases of the Libyan Desert have been frequently visited by travellers-Poncet in the seventeenth century, Browne in the eighteenth century, and Cailliaud, Drovetti, Edmonstone, Hoskins, Rohlfs, Zittel, Schweinfurth, Brugsch, and others in the nineteenth century-yet none of these authors enjoyed anything like the opportunities for the study of these remarkable districts which have fallen to the lot of the writer of the work before us. For nine years Mr. Beadnell, as a member of that active body the Egyptian Geological Survey, was engaged in the study of the Libyan Desert-including the four oases of Baharia, Farafra, Dakhla, and Kharga-while during the last three years, as director of the operations of a development company, he has resided in the last mentioned, and has carried out important observations and experiments in connection with the questions of water supply, the effects of moving masses of sand in increasing the fertility of some areas, while overwhelming and destroying others, as well as of many other problems of great historical and antiquarian interest.
Now that the opening of a railway from Qena, a little north of Luxor, to the village of Kharga has been completed, the long and tedious camel-journey of four or five days along very rough caravan routes is avoided, and excursions from the Nile valley to this typical oasis will doubtless become much more frequent. The appearance of the present work is, therefore, very opportune. The detailed topographical and geological survey of the Libyan Desert with its oases 1 "An Egyptian Oasis: an Account of the Oasis of Kharga in the Libyan Desert, with special reference to its History, Physical Geography, and Water Supply." By H. J. Llewellyn Beadnell. Pp. x+248; with 28 plates and 4 maps and sections. (London: John Murray, 1909.) Price 10s. 6d.
was undertaken in 1897-8. Mr. Beadnell carried out the mapping of the Farafra and Dakhla oases, while Dr. Ball was engaged in surveying that of Kharga. the work in the Baharia Oasis being shared between the two investigators. Dr. Ball's map of the Kharga Oasis, with the accompanying official report, is a work of great geological value and interest, and Mr. Beadnell's residence in the district has enabled him to add not a few important scientific details to the admirable sketch given by his colleague.
The whole Libyan Desert forms a plateau, having an elevation which, at its maximum, is but little less than 2000 feet above sea-level, yet with a fairly general slope towards the north. In this great expanse nf rough limestone and flint-covered flats. with hillocks and troughs of drifting sand, the oases are deep depressions, the bottoms of which vary from 100 to 300 feet above sea-level, surrounded, for the most part, by steep escarpments, through which only a few passes can be found which are capable of being used as camel-tracks. The whole of the deserts are underlain by great beds of sandstone (the Nubian series), forming two divisions, the surface-water sandstones," never more than 160 feet thick, separated by 250 feet of impervious grey shales, from a much thicker series of sandstones below, the "artesianwater sandstone," which has been penetrated by borings to the depth of 400 feet.
It is by the removal, through denudation, of great masses of Eocene and Upper Cretaceous limestones and shales that the " surface-water sandstones" have been exposed on the floors of the oases. These beds are the source of springs, and, since the districts have been occupied by human beings, a great part of the area of the Kharga Oasis was covered by shallow lakes, probably formed by the outflow from these springs. But these great lakes have been gradually dried up, and the constant drain on the limited supplies of water afforded by the "surface-water sandstones"
has greatly reduced its importance as a means of irrigation. The accounts of the various deposits laid down in these old lakes, with their interesting contents of worked flint-flakes and pottery, are among the most novel and interesting portions of Mr. Beadnell's book.
Far more important, however, than the surfacewater sandstones, as a source of irrigation water, are the "artesian-water sandstones,' which, by means of borings, have been drawn upon from the earliest times, and constitute even now a practically inexhaustible means for promoting the cultivation of the oases. On all questions connected with the nature and amount of the yield of the different kinds of wells, the author of this book writes as an authority, and he is able to give the results of numerous ingenious experiments, carried on, in some instances, for many months. That the enormous quantities of water contained in the thick sandstones of the Nubian system have their source, in part in the highlands of Abyssinia, in part in the Sudan, and to some extent in the upper waters of the Nile, where it flows over these pervious sandstones, there can be little doubt, though as to the proportional parts played by these several factors of the supply there is still much room for doubt a doubt which can only be removed by prolonged observations.
The manner in which the ancient wells have been made, kept open, and from time to time repaired, has engaged the author's attentive study. It is surprising to learn how much has been accomplished with the aid of very simple appliances; and the long subterranean aqueducts-tunnels driven for miles into the sandstones for the purpose of increasing the flow of water-with numerous manholes up to the surface,
are wonderful monuments of persevering toil. The introduction of modern boring machines and other labour-saving contrivances may probably do much towards increasing the productiveness of the land of these oases in the future. Very interesting information is given concerning the cultivation carried on in the Kharga Oasis, and its possible extension in the future. The chief crops at present are rice, date and doum palms, and lucerne, though grapes, oranges, and other fruits are produced to a small extent. Many of these fruits, with cotton and other useful vegetable products, may be largely supplied from these districts, now that communication has been improved by the construction of the railway. In spite of the traditions concerning the existence of deposits of gold, silver, and other metals in the oases, it is probable, considering the geological structure of the district, that it is never likely to yield mineral products of greater value than the ochre, alum, and epsom salts, which the ancients obtained in small quantities as the result of an altogether disproportionate expenditure of labour and pains.
The author, being evidently a keen sportsman, is able to give many interesting details concerning the feral life in these singular depressions of the desert. The
wild mammals consist of the Dorcas gazelle, with three species of fox, and occasional striped hyænas and jackals; the birds, of sand-grouse, rock-pigeons, turtledoves, and quail. But British sportsmen must be prepared to find, among the primitive inhabitants of these lands, competing sportsmen, as enthusiastic and probably more experienced and persevering than themselves.
Although it is to the questions of water supply, and the dependent problem of agricultural development, that we look mainly for information to this work, yet its author has not been unmindful of many other points of general interest concerning the population of 8000 to 9000 souls and its distribution. They belong to Berber tribes, quite distinct from the fellahin of the Nile Valley, but with admixture from various other sources, and the author has been able, during his sojourn among them, to learn much that is of interest about their habits and customs. Their personal characteristics, peculiarities of land- and water-tenure, their taxation and commercial methods are well described, and the features of their villages and farms are admirably illustrated. Their modes of combating their great enemy the drifting sands from the north, which tend to form ever-advancing sanddunes, receive especial attention. Some of the results attending this constant sand-drift are illustrated in the figures taken from the work.
Persian rule, Cambyses sent an ill-equipped expedition to conquer the oases, but the whole army of 50,000 men, probably through the treachery of guides, perished miserably in the desert. The Romans long held sway in the oases, and many of the most remarkable of the monuments of the district must be referred to the period of their rule. The work before us indicates the great numbers of objects of archæological interest which are found in the district, including many Græco-Roman temples and a wonderful early-Christian necropolis, as well as very early
The Egyptian kings, certainly from as far back as the eighteenth dynasty (1545-1350 B.C.), have claimed dominion over these oases. When Egypt fell under
flint implements and pottery. We learn that Mr. Pierpont Morgan has already had explorations commenced for the enrichment of American museums, and the completion of the railway may not improbably lead to excursions to Kharga and its temples becoming as popular as the trips to the cataracts and temples of the Nile are now. The book before us, which is dedicated to the memory of an old colleague of the author, Mr. Thomas Barrow, who fell a victim to the climate during explorations in the Sudan, ought to help to make known the points of interest attaching to these wonderful depressions in the great Sahara. JOHN W. JUDD.
THE ISLE OF WIGHT.
NOWHERE else in this country can the geologist
"Guide" contains a large number of
realising the difficult task that I was undertaking "; and he expresses himself content to have served as a "horrible example " if by doing so those who come after him are enabled to profit by his mistakes of omission and commission. Such modesty disarms criticism, and Mr. Morey's energy and enterprise deserve the warm thanks and congratulations of all who are interested in the natural his.ory of the Isle of Wight.
As is the case with all compilations, the book is unequal in quality, but we feel bound to point out two defects which, though common enough in works of this kind, detract considerably from its value and interest.
A book which attempts to compress into a comparatively small space an enumeration of the entire
FIG. 1.-The Culver Cliffs: Inset showing Heiring Gulls at their Nests. From "A Guide to the Nat :ra! History of the Isle of Wight." new records, and will at least form a good basis upon which resident and visiting naturalists may build a complete natural history of the district. There can be no question as to Mr. Morey's qualifications for the editorship of this volume, since he has worked at the fauna and flora of the island for forty years, and in producing the "Guide" has obtained the services of a capable band of systematists in the various branches dealt with. One cannot but admire his industry, versatility, and enthusiasm. He tells us, "when, nearly three years ago, I decided to bring out a work which should fairly illustrate the fauna and flora and the natural history generally of the Isle of Wight, I did so, almost literally, with fear and trembling, fully 1 "A Guide to the Natural History of the Isle of Wight." A Series of Contributions by Specialists, relating to the various branches of Natural History and kindred subjects. Edited by Frank Morey. Pp. xx+560.
fauna and flora of a rich district, with an account of its geology, to say nothing of articles on palæolithic implements, meteorology, and even earthquakes, must necessarily consist largely of a census catalogue of species. Lists of species are undeniably useful, and not to be despised when compiled carefully, but the ideal to be aimed at in a real natural history is surely something that shall go beyond, and in some respects be the antithesis of, a mere list. Beyond a few vague references to the bare fact that the distribution of species of flowering plants, mosses, &c., is affected by the characters of rocks and soils, we look in vain for any evidence of the scientific ecological spirit which animates such works as Baker's "North Yorkshire, Lees' "West Yorkshire," and Wheldon and Wilson's "West Lancashire," and has made them valuable
(Newport, I.W.: County Press; London: W. Wesley and Son, 1909.) contributions to the growing literature of plant
Price 8s. 6d. net.
ecology. The three books cited are, of course, limited
to the botany of each district, but a general sketch of the distribution of the flowering plants, at any rate, should have been given in this "Guide." The island would afford excellent scope for a botanical survey, on the lines of the well-known work done by Dr. Smith, Dr. Moss, and other ecologists, in various parts of Britain. It is greatly to be hoped that in a future edition of, or supplement to, this Guide" it will be found possible to include a chapter on plant distribution, with a vegetation map of the island, and, for comparison and correlation, a geological map. This would, if carefully done, preferably by an ecologically minded botanist residing in the district, undoubtedly enhance the value of the book and secure for it more than the local interest that attaches to a merely floristic work.
string of incoherent and inaccurate sentences, repeating and perpetuating long since exploded errors and mare's-nests. Lichenologists, we know, are a stiffnecked generation, but surely it is time they hesitated to record in print their refusal to recognise the dual nature of the lichen thallus, which has been fully and finally established. There can be no excuse, either, for the hepaticologist who tells us that the liverworts are "linked to the lichens" by means of their thalloid forms! The account of the relationship between the liverwort Frullania and the rotifer which sometimes occupies its pitchers is entirely imaginative. The list of hepatics (liverworts) is conspicuous by the omission of several species which are certainly found in the island, and often abundantly in places, such as Anthoceros laevis, Scapania nemorosa, and Lepidozia reptans.
The articles by Mr. G. W. Colenutt (geology), Mr. P. Wadham (fishes, mammals, &c.), and Mr. R. H. Fox (birds) stand out as refreshing oases in the arid desert of species lists, being written in a "naturestudy spirit which can hardly be said to characterise the work of the other contributors. The "Guide" is illustrated by twenty-six excellent plates, chiefly from photographs by Mr. H. F. Poole, two of which we are permitted to reproduce here. F. C.
[H. F. Poole.
FIG. 2.-White Stork-a rare visitor-captured at Shorwell in 1902.
Iing sickness is due to infection with a trypanosome (Trypanosoma gambiense), and that this trypanosome is conveyed by a tsetse-fly (Glossina palpalis). But if we proceed to analyse and extend this proposition we soon get into difficulties. We do not know for certain whether man is the only "reservoir" of this trypanosome, or whether monkeys and other mammals, especially native dogs, can also harbour it. Should this prove to be so-though the balance of evidence is against the supposition-it must materially affect prophylactic measures. If we consider next the mode by which the trypanosome is conveyed we find ourselves in the midst of the most conflicting evidence. It is still uncertain whether the transmission is mechanical or whether there is a cycle of development 2 of the trypanosome in the fly; facts appear to be all in favour of the first view, analogy all in favour of the latter. Nor is the question a purely academical one, for if the transmission is mechanical, then the flies are no longer infective after the infecting reservoir (man) is removed; if, however, there is a cycle of development, then it remains to be determined how long an infected fly can remain infective after the infecting source is removed.
T may be taken as definitely established that sleep
If, again, we consider the question, Can sleeping sickness be conveyed by any other species of tsetseFrom fly than Gl. palpalis? we must confess our ignorance. The balance of evidence certainly seems to be against the possibility, but should it be shown that other species can convey the disease, then the question of prophylaxis would be even more difficult than it now is. These reports show that these are some of the questions that urgently need solution, but there are others of equal importance which arise in the immediate carrying out of prophylactic measures. They concern the fly itself, its habits, duration of its life, its breeding grounds, its food, its powers of flight, its likes and dislikes in regard to foliage, trees, shrubs, grass, &c. These questions are all important, and
The second suggestion we venture to make, with reference generally to books similar in scope to this Guide," is that most of the systematists responsible for the various lists of plants and animals given in local naturalistic compilations would do well to obtain the cooperation of a biological botanist or zoologist when writing their prefatory remarks on the group of plants or animals they are dealing with. So far as this "Guide" is concerned, we refer chiefly, as examples, to the sections dealing with some of the cryptogamic plants. It would be far better for the average cryptogamic systematist to pass straight on to his list and say nothing whatever about the lifehistory and development of his group than to write a
1 "Reports of the Sleeping Sickness Commission of the Royal Society." No. ix. 2 The existence of such a cycle is now practically established by the recent work of Kleine confirmed by Bruce.
in our opinion it is imperative to appoint one or more officers with special entomological knowledge to study these points minutely. It is true that these reports afford evidence that the officers concerned in these investigations have made additions to our knowledge on these points, but the other duties of these officers are so multifarious that valuable time is being lost through this defect. It is true also that in the epidemic in Uganda the condition of things is so terrible that it is impossible to wait for the solution of all these questions, however important, before any action is taken, and we may now consider what, with the present available knowledge, is being done to check the epidemic. The means of prophylaxis may be considered under three aspects :-(1) Those directed against the fly; (2) those directed against the carrier of the trypanosome, i.e. man; (3) those directed against the trypanosome itself.
(1) With regard to measures directed against the fly. It has been found, and it is a matter of the highest importance, that the "natural range" of the fly, i.e. the distance to which flies follow from water in search of blood, is, as a rule, under 50 yards. The still more important fact has been determined that clearing and burning or removing the undergrowth for a distance of 100 yards in either direction, e.g. from a ferry for a strip 50-100 yards broad, has the effect of banishing the fly. It is this method, then, i.e. banishing the fly by clearing from its "normal fly range," that is the basis of the methods now being carried out in Uganda. It is not necessary to clear extensively around a village, but simply to clear comparatively small strips of the " fly range "frequented by man.. Although flies may occur in the village itself, unless there is a "fly area" present these flies are those which have followed their victims beyond the "fly range to the village. If the flies of the "fly range" are banished, then, ipso facto, the "following" flies also disappear. A typical fly area, though there are exceptions, consists of more or less open water with contiguous and especially overhanging shade and generally a fairly well-defined bank or shore. If, then, clearing can permanently banish the fly, and we believe that this will be found to be the case, because the fly still has plenty of uncleared area to frequent-though the fact that its human blood supply is at the same time removed may modify the result it is an important measure of prophylaxis, though its value is perhaps restricted to somewhat small areas and special conditions.
If the fly cannot be removed by clearing, then the population must be deported from the vicinity of the fly. This measure has been extensively carried out in Uganda by the removal of populations from the lake to inland fly-free areas two miles away, to prevent traffic from the lake, which is responsible for the great bulk of the infection; but in many cases there are serious difficulties in the way. Further, the removal of populations still non-infected from a potentially dangerous fly area to a safe fly-free area would be of the greatest importance, and would form a more striking object-lesson to the native of the value of these measures than the removal of an infected population, because a certain, probably high, percentage of these latter will eventually die of sleeping sickness, although in a safe area; whereas this would not be the case if the population removed was non-infected.
(2) As the two measures, clearing and deportation, of the healthy, are undertaken with the object in view of preventing access of the fly to man, so segregation of the sick prevents fresh infection of the fly, and diminution of the infectivity of the fly in a fly area. This implies the removal of the sick of a village to another village or camp in a fly-free area, and it is
important to note that such areas are numerous, and may often be only a few hundred yards away. Fresh infection of the fly is also avoided by preventing the removal of infected natives to uninfected fly areas. The applicability of this measure depends mainly upon the "attitude" of the native.
(3) Measures directed against the trypanosome itself, i.e. the treatment of infected persons, are bound up closely with the segregation of the sick. The trea ment of the segregated in fly-free areas by atoxyl or other arsenic preparations is the only one that is at all effective, but it must be admitted that the results are disappointing, and that the good results of the drug are in many cases only temporary. The patient's blood becomes free from trypanosomes (and presumably non-infective, though this is not proved), and so the chance of infection of the fly, if patients come in contact with fly areas, becomes less.
Time will show how far these measures, the numerous important details of which we have to leave unconsidered, will be successful. Those engaged in carrying out these arduous and dangerous measures have hope that although sleeping sickness may not be eradicated or the fly totally annihilated, yet that the epidemic will soon be under control. It must be the sincere wish of everyone that this hope may be justified. J. W. W. S.
THE CONTAMINATION OF MILK. THE contetailed research by Dr. Orr, carried out contamination of milk has been the subject
on behalf of the councils of the county boroughs of Bradford, Hull, Leeds, Rotherham and Sheffield, and the administrative counties of the East and West Ridings of Yorkshire. Of previous investigations, Delépine concluded that though his results did not exclude the possibility of infection at the home of the consumer, or during transit from the farm, they did indicate that infection at the farm, or through vessels infected at the farm and used by the farmer for the storage and carriage of milk, was of para mount importance. On the other hand, Newsholme attaches little importance to infection at the cowshed. Dr. Orr's investigation was carried out in a systematic manner, and not only were the bacteriological examinations carefully performed, but, in addition, the condition of the cows and cowsheds and the effects of season and atmospheric temperature were noted. First, the bacterial content of the milk in the udder was estimated, and it was found that the fore-milk (that first milked) contained from 18,000 to 48,000 microorganisms per cubic centimetre, and the milk after the removal of the fore-milk 890 to 4800 per cubic centimetre.
It is generally agreed that the milk as secreted is sterile, the microorganisms in the milk as drawn being derived from lodgment and multiplication in
the teats and cistern.
Dirt on the udder is a fruitful source of contamination, and, during milking, dust, &c., from the udder adds much to the bacterial content of the milk. Dust in the cowsheds, and the entrance of dirt during transit and delivery, further add to the contamination. so that the milk, when it reaches the consumer, may contain an appalling number of microbes. The chief conclusions derived from Dr. Orr's work are:
(1) Of the total organisms in the milk used by the conDuring railway transit, at the retailer's premises, and in sumer, the greatest number are contributed by the farmer. the consumer's house, smaller amounts are added, the amount in each instance being apparently about the same.
(2) Of the glucose-fermenting or intestinal organisms and the streptococci, by far the greatest number are added