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THURSDAY, MARCH 11, 1915.

A TEXT-BOOK OF FORESTRY. Elements of Forestry. By Prof. F. F. Moon and Prof. N. C. Brown. Pp. xvii + 391. (New York: J. Wiley and Sons, Inc.; London : Chapman and Hall, Ltd., 1914.) Price 8s. 6d.

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HE progress of forestry in the United States is remarkable. It is barely twenty years since the first forest reserve was set aside by the Government at Washington, which to-day controls with a trained staff of foresters about 186,000,000 acres of national forests. Forestry is now a matter of great public interest, and is taught in universities, colleges, and schools, there being no fewer than twenty-three institutions giving degrees in the subject. In addition to numerous bulletins and reports issued by the U.S. Bureau of Forestry, there now appear two professional journals, the Forest Quarterly and the Proceedings of the Society of American Foresters. Various text-books on special branches of forestry have been published, but no general handbook suitable to students in America has hitherto appeared.

"Elements of Forestry," by Moon and Brown, is an attempt to supply this need, and it is very satisfactory as an elementary text-book. It will serve as a good introductory work for professional students of forestry, and covers about as much of the subject as is necessary for students in agriculture. The book is clearly printed and well-illustrated. All the usual divisions of the science and art of forestry are taken up in a series of simple and attractive chapters, at the end of each of which is a short and useful bibliography. Of chapters i. to xiv., which are of universal application, those devoted to the utilisation, technology, and preservation of wood are of special interest; and much praise must be given to the chapter on forest finance, in which the gist of this important matter is expounded in sixteen pages. The attention of landowners and practical foresters may be directed to the example on p. 265, which illustrates the most common problem in forestry finance in England, namely, the estimate of the cost of raising a crop of trees to any given number of years of age, and incidentally determining whether a plantation is a profitable investment or not.

Chapters xv.-xxii., entitled "Regional Studies," deal with the conditions of the forests of the United States, which are divided into seven regions. The description, silviculture, protection, and utilisation of the forests of each region are briefly but adequately dealt with. At the end of

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MR.

R. NORTHCOTE THOMAS has given us an exceedingly interesting piece of work in African philology by publishing for a reasonable price what might be called a sketch of the languages of Southern Nigeria between the frontier of the Bantu Cameroons on the east, and the Yoruba country on the west. The same ground was covered in 1888 by the writer of this review, but his work, which would be of interest in comparison with, and supplementary to, that of Mr. Northcote Thomas, was only privately printed by the Foreign Office. Perhaps some day it may be disinterred from a confidential blue-book and produced with other linguistic studies.

Mr. Thomas's specimens (prominent nouns, numerals, pronouns, and such syntax as can be illustrated by a variety of sentences) include nearly the entire range of the Ibô dialects, the languages of the Calabar and Cross River district; the Ijō of the actual Niger mouths, Yoruba of the Lagos vicinity, Sôbô and Kukurúku of the Bini-Edo group, Ibibio of the region between the Calabar estuary and Opôbô, and a number of very interesting semi-Bantu languages on the verge of the Cameroons frontier. Mr. Thomas does not attempt much in the way of classification, but would seem to indicate that he finds a connection more or less close between the semiBantu Yala, which lies far to the north of the upper Cross River, and the Edo or Bini group in the western part of Southern Nigeria. No evidence of very close affinity, or of affinity at all, is to

be deduced from the actual vocabularies given. Personally, I should have been inclined to regard Yala (which is one amongst Koelle's many interesting vocabularies of 1854, hitherto difficult to locate geographically) as having nothing to do with Edo, but much with the more "semiBantu" speech contiguous to it on the east. Not the least interesting part of this useful manual is the identification and location of eighteen of Koelle's vocabularies, work which greatly enhances their value to the philologist. In addition, Mr. Thomas introduces us for the first time to several speech forms-languages and dialects hitherto unknown.

Mr. Thomas's work throws a good deal more light on the semi-Bantu languages in addition to the not-sufficiently-known work of Mr. P. Amaury Talbot. The analysis of the material his vocabularies furnish induces me to account for the semi-Bantu group and cognate languages in two ways:-Some of them, especially in the east and south of their range, may be simply much-worn-down and corrupted real Bantu; relics of the comparatively ancient east-to-west migration, which finally carried a Bantu speech to the Island of Fernando Pô. But the balance of probability, especially in regard to the more northern groups of semi-Bantu, lies in the direction of their being descended from sister languages of the original Bantu mother tongue. They would thus have migrated from north-east to south-west. All such indications seem to lead to the theory that the original home of the Bantu was somewhere in the very heart of Africa, between the basins of the Benue, the Shari, the Mubangi and the Bahr-al-Ghazal. But Mr.

Thomas's work further directs our attention to the existence of Bantu roots in Ibô and Gori; and this ancient Bantu influence can, I believe, be traced much farther to the west than the lower Niger. H. H. JOHNSTON.

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U.S. Department of Agriculture, by Dr. L. O. Howard and Mr. F. H. Chittenden, on pests of this nature, in 1896, much work of importance has been done, particularly, with regard to houseflies and mosquitoes. Students of the subject should, therefore, be grateful to Prof. Herrick for providing a popular and trustworthy account (1) of our arthropodous "messmates" and parasites. In addition to insects in the zoological sense of the term, spiders, mites, ticks, solpugids, scorpions, and centipedes are passed in review, and the British reader cannot but feel that some compensation for not being an American is afforded by the comparatively scanty housefauna of his native land.

The especial strength of Prof. Herrick's book lies in the directions given for dealing practically with the various pests; systematic and bionomic considerations are, throughout the volume, subordinated to the economic point of view. No fewer than one hundred pages are devoted to house-flies and mosquitoes; the disease-transmitting power of these insects is emphasised, albeit with the minimum of information as to the nature of the micro-organisms that they carry. Doubtless the author has been well advised to lay stress on the habits of the creatures that he describes in their relation to remedial and preventive measures, but if a little more space could have been devoted to the zoological aspects of the subject, the reader would take a more intelligent interest in the practical problems brought to his notice. Each chapter is followed by an "economic" bibliography, and the book is illustrated by more than 150 figures of somewhat unequal merit.

(2) Dr. Gordon Hewitt has, by his researches since 1907, made the House-fly (Musca domestica), to an especial degree, his own subject, and his transference from Manchester to Ottawa has not cut him off from an abundant supply of material of this cosmopolitan insect. In the handy volume now before us, all the anatomical and histological descriptions and figures from Dr. Hewitt's previously published works are collected in a convenient form, and a full survey of the latest literature on the house-fly and allied Diptera, together with an account of Dr. Hewitt's own recent investigations, will be found to furnish a store of information for the student. Interest in house-flies during recent years has centred around the possibility of these insects serving as carriers of disease-germs to human food-products, and the critical survey of the newest work on this subject-especially with regard to the prevalence of infantile diarrhoea during the fly seasonforms a most valuable section of Dr. Hewitt's

for

book. Experiments carried on at Ottawa on the distances travelled by marked flies showed various ranges of flight up to 700 yards; observations quoted as made by Dr. Copeman in rural districts in Norfolk give a flight-range of 1700 yards. The book concludes with a discussion of the best methods for destroying fly-maggots and for checking the facilities for the breeding of the insects. Bavaria enjoys the reputation of a noteworthy paucity of flies, "perhaps due to the extreme cleanliness of Bavarian cities." Dr. Hewitt's book can be most heartily commended to all enthusiasts on behalf of public health, as well as to students of the anatomy and life-history of insects. G. H. C.

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E. J. S. Lay. England and Wales, pp. 80. Price 4d. The British Isles, pp. 118. Price 6d. The British Dominions, pp. 128. Price 6d. (London: Macmillan and Co., Ltd., 1914.) (3) Macmillan's Geographical Exercise Books. With Questions by B. C. Wallis. i., The British Isles, pp. 48. Price 6d. ii., Europe, pp. 48. Price 6d. Price 6d. iii., The British Empire, pp. 48. Price 6d. (London: Macmillan and Co., Ltd.)

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(5) The Map and Its Story. Pp. 44. (London: G. W. Bacon and Co., Ltd.) Price 1s. net. (1) NCE the pupil or student gets past the general outlines and principles of geography (which are so difficult for the author and teacher to lay down in terms that are otherwise than summary and dull), he ought to find out the real interests and fascination of the subject. A book like Mr. Taylor's will help him to do so. This writer has an unusual faculty for keeping steadily in view the interaction of those phenomena which geographers set out to study, and for picking out the right facts from the special departments of knowledge on which geographers have to draw. He also sets great store by the use of the map to illustrate special points, and in this direction shows considerable originality; the maps are generally clear, though sometimes injudiciously reduced, and occasionally rather severely generalised. The descriptive and explanatory writing could not well be clearer,

and this being so, the author is safe in carrying his readers into such unaccustomed topics as that of the paragraphs in which he discusses the former history of river courses and the extent of land, a "journey into past geological times" which is justified, as he is able ingeniously to show the bearing of former physical conditions upon modern communications. This book would be an excellent introduction to Australasia as a special subject.

(2) Both the manner and the matter of Mr. Lay's three little volumes, according to their lights, are fairly satisfactory, and a large number of questions and exercises are provided, many of which will carry the pupil well beyond the scope of the work, and are properly suggestive. Others tend to throw back to the old narrow field of geographical teaching, demanding merely a list (e.g., of "the highest mountains of the Pennine Chain "), while it is difficult to conceive in what possible geographical connection such a question is asked as, "Do you know the name of a Councillor? A Magistrate?" Pieces of poetry are set for learning, but the geographical value of poetry is too often doubtful, especially when its language is as difficult as that of W. J. Mickle's translation of Camoens. The text of these books illustrates at some points one of the geographer's besetting dangers, generalisation; such sentences as "Edinburgh, which is built on the famous Castle Rock"; "The Dominion of Canada is provided with a splendid system of waterways"; in the same country "the various minerals-with the exception of . . . gold and silver-are scarcely worked," are statements which, in the want of qualification, may be highly misleading.

The maps (black and white) in this series are commendable, though we should hesitate to subscribe to the claim that "no atlases or other maps" are "required." A point of some interest emerges on making a comparison of maps in this series in Mr. Taylor's book, and in "The Map and Its Story," presently to be noticed. The desirability is revealed of some attempt at standardising distribution maps. The maps illustrating the vegetation of Australia in these three books are, it is true, laid out on rather different systems, but their methods are sufficiently similar to show how widely divergent are the results obtained. A pupil comparing the three would be excusably "floored" in attempting to gather from them the extent and locality of forest and desert areas, and so forth, in Australia, and the differences are such that one or more of the maps must be very seriously in error.

(3) Mr. Wallis's "Geographical Exercise Books" consist of blank maps (sometimes with contour lines), and on the page facing each map a series of questions or directions as to filling it up and writing notes or exercises on the results obtained and the conditions revealed. Both maps and letterpress appear to be very judiciously chosen or compiled, and in the hands of a pupil of moderate capacity in draughtsmanship the finished product should possess a permanent value.

(4) Messrs. Bacon's "Sixpenny Contour Atlas' is very good, considering its price. It contains thirty-two coloured maps, showing the elevation. of the land according to a recognised method, and dealing with the world and its various divisions, in addition to which there are a few maps of a special area, varying according to the pupil's requirements-e.g., the edition under notice is that for south-east England, and contains special maps of that district, while editions for south Scotland, south Wales, and others are promised.

(5) The same firm's publication, "The Map and its Story," does not maintain the standard of the work previously noticed, so far as concerns its coloured maps illustrating climate, vegetation, etc. Some of the printing (e.g., of the natural resources shown in red lettering) is bad, and some of the distribution colouring weak. But the distinctive feature of the work, the letterpress accompanying the maps, explains them very clearly, and ought to fulfil the purpose of guiding students as to what they should look for and find, not only on these, but on other maps.

OUR BOOKshelf.

Huxley Memorial Lectures to the University of Birmingham. With an Introduction by Sir Oliver Lodge. Pp. 164. (Birmingham:

Cornish Brothers, Ltd., 1914.) Price 55. net. Of the nine memorial lectures which have been delivered, the present volume contains only five. That by Prof. Joly on pleochroic halos does not even mention Huxley's name. Sir Oliver Lodge leads off with Huxley's own defence against the charge of materialism. "There is a third thing in the universe which . . . I cannot see to be matter or force, or any conceivable modification of either." This was consciousness. Sir Michael Foster found in Huxley the "conviction that what began as a search into things physical has become a search into things spiritual." Prof. Poulton points out that Huxley "never committed himself to a full belief in natural selection, and even contemplated the possibility of its

ultimate disappearance." We come, in the remarkable paper by Prof. Percy Gardner, to the pith of the matter, "in regard to which words from Birmingham are greatly valued, the study of the subconscious side of man."

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Prof. Bergson's lecture on life and consciousness traverse's a field antipodal to that of Huxley. Consciousness is "the mind." It "and It is at once a matter are antagonistic forces." "creative force," a "vital impulse," and a 'spiritual force. Life is "nothing but consciousness using matter for its purposes. It "cuts it up in order to bring about a greater precision." The evolution of life . . . suggests to us the image of a current of consciousness which flows down into matter as into a tunnel." The final conclusion is "that with man consciousness has

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finally left the tunnel" to "pursue its path beyond this earthly life."

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Dew-Ponds-History, Observation, and Experiment. By E. A. Martin. Pp. 208. (London : T. Werner Laurie, Ltd., n.d.) Price 6s. net. A DIFFICULT problem has been attacked by Mr. E. A. Martin in this book. He defines a dew-pond one situated on the higher grounds, generally on the chalk downs of the south of England, which retains by some means or other a supply of water throughout all but the most prolonged droughts. whilst those ponds situated on the lower lands have consistently dried up." With the aid of continuous observation, and a grant from the Royal Society for experimental purposes, he has been able to throw much light on these curious ponds. He shows that "dew-pond" is a misnomer, for dew is quite insufficient to make up for loss by evaporation; and he inclines to the use of the term "mist-pond" as better explaining their origin. However, "dew-pond" is in common use, and when farmers speak of dew they include the condensation of mist and cloud also.

The author suggests that the small crystals of sodium chloride, found in sea air, have acted "as nuclei of condensation when the night-mists form on the downs, and as the mists blow up in the early morning from the sea they pass across the pond-depressions and are deposited in quantities there." Certainly it is to the morning mists drifting in from the sea that the replenishment of these ponds is mainly due. We would direct particular attention to some of the observations, in which are given actual measurements of the amount thus deposited. It is noticeable also what a large part is played by rushes or other vegetation in increasing the deposition. However, aspect, slope of ground, and other things all play their part, and great care is needed in the selection of a site.

We recommend this book to the notice of engineers and others who have to do with hilly regions where rain is deficient, but where heavy mists are common, as, for instance, the Pacific slopes of the Andes.

LETTERS TO THE EDITOR.

[The Editor does not hold himself responsible for opinions expressed by his correspondents. Neither can he undertake 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 communications.] Resonance of Sodium Vapour in a Magnetic Field. Ir is well known from the observations of Wiedmann and Schmidt, Wood, Dunoyer, and others that dilute sodium vapour contained in a glass bulb emits resonance radiation when a soda flame is focussed upon it. During the last few days I have examined the effect on the resonance radiation of putting the resonating vapour in a magnetic field.

If the exciting flame contains very little soda, the resonance radiation is diminished by the field.

If, on the other hand, the flame is rich in soda, the field greatly increases the resonance radiation.

It is too early to put forward more than a tentative suggestion towards the explanation of these effects. Each sodium line emitted by the resonating vapour is broadened by the Zeeman effect. The flame poor in salt gives a narrow exciting line, and magnetic broadening throws a part of the resonating line off the exciting line, thus diminishing the light.

Adding more salt to the flame makes each exciting line broader, and (it is provisionally assumed) reverses the middle of it. Thus magnetic broadening of the resonance line tends to bring the brightest parts of the exciting line into action, and increases the light.

It may be remarked that with an intermediate condition of the flame a moderate field would produce the kind of effect last referred to, while a very strong field would separate the side components so far as to throw them beyond the limits of the exciting line. An effect of this kind has been observed, though unfortunately the condition of the exciting flame at the time was not noted. The current was switched on, and as the field increased (this takes a perceptible time) the resonance radiation increased and then diminished again. On turning the current off, the light again passed through a maximum. The greatest strength of field used in this experiment was about 14,000 units. Brightening can be distinctly observed with 1000 units, when a well-salted flame is used.

I have not been able to find that any previous observations have been made on the resonance of sodium vapour in a magnetic field. Observations were made on mercury vapour by Malinowski (Phys. Zeits., September, 1913). The present experiments were suggested by some made in this laboratory by Mr. F. S. Philipps on mercury vapour (see NATURE, December 4, 1913). His observations were independent of Malinowski's. R. J. STRUTT. Imperial College, South Kensington, March 9.

The Spectra of Hydrogen and Helium. DR. BOHR's letter in NATURE of March 4, although giving an interesting discussion of some aspects of this problem, does not meet the particular point which my letter was designed to raise. This point was solely that since combination series must be expected from the "4686" series in any circumstances, and since the lines so calculated occupy the positions in which lines have been found by Evans, they cannot be used to discriminate between theories of the origin of spectra, for we cannot prove that the observed lines are not these combination lines. It is true that Bohr's theory involves the combination principle, but so also does that of Ritz, who originated the principle. My letter (NATURE, February 11, p. 642) took up

this purely negative attitude, and was not intended as a criticism of the theory. It did not even advocate a hydrogen origin for the lines. Fowler's view, that the "4686" series is a 4N series analogous to that in magnesium, was, in fact, stated to have more evidence in its favour. Whether the origin be really hydrogen or helium is not actually relevant to my argument. Even if the origin is really helium, it was pointed out by Fowler in his Bakerian lecture that his results do not formally imply Bohr's theory. Since that time, the writer has published a proof that the theory cannot explain 4N series in general, for such elements as magnesium. It can only deal with helium, and the formal analogy between helium and magnesium would weaken, rather than strengthen, the theory.

The greater part of Dr. Bohr's letter does not bear on my original point, for he is seeking to discriminate between a hydrogen and helium origin, and between his view and Rydberg's, not directly by Evans's experiments, but by other considerations. At the risk of going further from the point at issue, I feel that some remarks on these considerations are necessary.

The references to Rau's experiments on voltages necessary to produce series are interesting, and if they have been interpreted correctly-there is some doubt of this-they show that the chemical origins of the series are those stated by Dr. Bohr, and by Stark and others. They show also that the electrons in Bohr's model atoms have the proper angular momenta. There are other reasons for believing that the relation of the atom to Planck's his contained in the angular momenta, and such atoms were treated by the writer some years ago, but with a different kind of emission. Nevertheless, Rau's experiments have nothing to do with the mechanism of spectral production, and cannot support any theory of the mechanism of radiation. For the radiation problem is quite superposed on any specification of the steady configurations of non-radiating atoms.

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The remarks concerning Rydberg's view proceed throughout on the supposition that the usual constant u-Rydberg's phase-is zero in these series. such case is known elsewhere in the whole range of spectra. It is quite easy to fit the "4686" series into a formula exhibiting it as a principal series of hydrogen, if this constant μ is not arbitrarily chosen as zero. There are other arrangements of the disputed series as hydrogen series which are formally possible, but their description would occupy too much space here. A full account of the whole problem will be published shortly, so that I propose to discontinue the present discussion with this letter. Meanwhile a protest must be urged against Dr. Bohr's conviction that the spectrum of atomic hydrogen consists solely of the Balmer, Ritz, and Schumann series. For MM. Fabry and Buisson have shown that a very large number of lines in the "secondary" spectrum are due to atoms of hydrogen. A correct model of the hydrogen atom must account for more emission spectra than have yet been deduced by Bohr's theory. Finally, I must again state explicitly that my present purpose is not to call the theory into question. My only concern is to show that no decisive factor has yet entered, and that judgment between theories must at least be suspended for the present. The importance to physics in general of the whole question of spectral emission is so great that a hasty decision must not be made. And the fact remains that all the present experimental results are explicable in widely different ways. The test mentioned at the end of my previous letter still appears to be an obvious crucial one. J. W. NICHOLSON.

University of London, King's College, March 5.

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