186 



KNOWLEDGE. 



[August, 1908. 



genie, origin ; and tbis could scarcely fail to be tbe case." An 

 immense amount of materi:il wbicb lends itself to exact analysis 

 in tbis way is contained in Dr. Vernon's book, and it all tends 

 to promote tbe scientific study of variation. Tbe volume is a 

 most valuable contribution to tbe literature of natural science. 



"Geometrical Optics." By Thomas H. Blakesley. Pp. vii. 

 and 12:5. (London : Whittaker & Co. ]9o:i.) 2s. 6d. net. 

 Illustrated. — Students of optics will find many instructive and 

 original ideas in this book, though tbe prime object of its publi- 

 cation appears to be a protest against the definition of focal 

 length usually accepted. The focal length of a lens is defined 

 in many books on optics as the distance of tbe principal focus 

 from tbe posterior surface of tbe lens, but this definition is 

 unsatisfactory, and Mr. Blakesley fathers ujion it many imper- 

 fections of optical instruction, design, and testing. Lenses 

 which have a negative value for their focal length are considered 

 in general as convex lenses, while those which have positive 

 focal lengths are regarded as concave ; but these terms are 

 .shown to be illogical because " a double convex lens of equal 

 curvatures, if sufficiently thick, will have a positive value for its 

 focal length with tbe general properties of a concave lens.'' By 

 measuring distances of object and image from the first and second 

 ])iincipal foci instead of tbe principal points, difficulties are 

 avoided; and simple mathematical forms are developed which are 

 true not only for a simple lens, but also for two or any number 

 of lenses having a common axis. Novel optical experiments are 

 described for determining tbe positions of the principal foci and 

 the focal length, and formulie are given, which, with a know- 

 ledge of the thickness of the lens, enable all the remaining 

 structural details to be found, namely, the two radii of curva- 

 ture and the index of refraction. The book should be tbe 

 means of increasing the precision with which optical details are 

 measured and expressed. 



"Natural Law in Terrestrial Phexomexa : A Becord 

 OF Evidence.'' By William Digby, c.e. Pp. xlv. and 370. 

 (London : W. Hutchinson & Co.) Illustrated. — No useful 

 purpose would be served by a detailed criticism of this book, 

 so we will briefly describe the chief points put forward, for 

 whatever we might say concerning the theories described would 

 be regarded as opposition which traditional schools of scientific 

 thought present to novel ideas from laymen. The book contains 

 a detailed statement of Mr. Hugh Clements's theories and pre- 

 dictions relating to weather and other terrestrial phenomena. 

 " I believe," says Mr. Digby, " that the succeeding pages of this 

 book prove that the moon's attractive influence exerted upon 

 the earth's atmosphere, in conjunction with the sun, accounts, 

 in the main, for all weather phenomena." For particular 

 positions of the moon and sun jointly, certain conditions of 

 weather are prescribed, so that weather prediction becomes an 

 easy form of study of orbital movements. To avoid misrepre- 

 sentation we quote from the formula upon which Mr. Clements 

 bases his forecasts. " Thus it follows that barometric pressure, 

 increase or diminution of clouds, much or little sunshine, an 

 overplus, an average, or a scanty supjily of rain, earthquake- 

 shocks, volcanic eruptions, will ail occur in time to come as they 

 did in times past, so long as, in the case of shocks and eruptions, 

 weak spots remain in the earth's crust." It would be easy to 

 offer objections to many parts of the argument upon which 

 this conclusion is based, but we will confine ourselves to one 

 point. It is that human interference is a factor which makes 

 it impossible to reduce weather prediction to tbe mechanical 

 conditions described. A man drops a lighted match on a dry 

 ])rairie, or leaves the smouldering embers of a fire in a forest. 

 A great conflagration occurs which may disturb the atmospheric 

 currents for hundreds of miles. It is imjiossible for Mr. 

 Clements or any other meteorologist to predict the effects of 

 this and similar disturbing causes. But Mr. Clements may rest 

 assured that if his theories are true they will survive scientific 

 opinion ; if, however, as we think, they are unsound, they will 

 eventually be relegated to the limbo of the paradoxers. 



" Volcanic Studies in Many Lands." By Tempest 

 Anderson, M.D., F.G.S., etc. (Murray.) 21s. net. — Dr. Anderson 

 is so well known as a photographer of and student of volcanic 

 forms that this handsome book cannot fail to meet with a 

 hearty welcome. Readers of Geikie's " Ancient Volcanoes of 

 Great Britain" and of Bonney's "Volcanoes" are already 

 familiar with his work, and, through Dr. Anderson's courtesy. 



we were enabled to reproduce two of his recent photogi'aphs of 

 Mont Pelre in Knowi.eix^e for last November. The iiresent 

 volume is the result of expeditions made during the last eighteen 

 years to Vesuvius and Etna, tbe Eifel and the Auvergne, the 

 Lipari Islands, the Canary I.slauds, Iceland, and the West Indies, 

 as well as to various regions in Britain and North America, in 

 which volcanic action has for long ages been extinct. It con- 

 tains more than a hundred plates, each accompanied by a short 

 description. The photographs from Iceland, Rhenish Prussia, 

 and St. Vincent are, perhaps, of exceptional interest ; but the 

 whole series is unrivalled in the illustrations it affords of the 

 various details of volcanic structure. 



" Tsi.MSHiAN Texts." — From the Smithsonian Institute we 

 have received a copy of a volume (No. XXVII.), of the Bulletin 

 of the Bureau of American Ethnology, devoted to the elucida- 

 tion of the so-called Tsimshian Texts, by Mr. F. Boas. Although 

 the transcript of these texts is doubtless of much interest 

 and importance to the students of folk-lore, it is not of a nature 

 to attract the majority of our readers. We must therefore pass 

 over the volume with this bare mention. 



BOOKS RECEIVED. 



British Sainfall, 1902. By H. Sowerby Wallis and Hugli Robert 

 Mill, D.sc, I.L.D. (Edward Stanford.) lOs. 



The Junior Arithmetic. By R. H. Chope, b.a. (University 

 Tutorial Press, Limited.) 2s. 6d. 



Sand-Buried Ruins of Khotaw. By M. A. Stein. (T. Fisher 

 Unwin ) 21s. iiett. 



A Short Manual of Atialiftical Chemistry. By John Muter, pu.d., 

 F E S.E., F.I c, F.c.s. (BailUfere, Tindall & Cox.) 6s. nett. 



The Structure of the Nucleus. By Carl Barus. (Smithsonian 

 Institution.) 



Etude Sur L'Appareil Circumz/nithal. By Fr. Nusl et Josef Jan 

 Frie. (L'Academie des Sciences de L'Empereur Francois Josef I.) 



A Brief Course in Qualitatire Chemical Analysis. By Jolin B. 

 Garvai, U.S. (D. C. Heath & Co.) 3s. 6d. 



Elements of Physics. Bv Fisher and Paterson. (D. C. Heath 

 & Co ) 23. 6d. 



Ways of the Six-Footed. By A. Botsford Comstock. (Ginn&Co.) 2s. 

 The Truth about the Egypt Exploration Fund. Uy William 

 Copley Winslow, d.d., d.c.l., ll.d. 



Meteorological Observations made at the Perth Observatory and 



other places in Western Australia, under the direction of W. Ernest 



Cooke, M.A., F.R.A S., Oovernment Astronomer. (W. A. Watson.) 



An Introduction to Botany. By Wm. Chase Stevens. (D. C. 



Heath & Co.) 6s. 



Elementarii Phqsioloqy and Hygiene. By Buel P. Colton, m.a. 

 (D. C. Heath & Co.) 2s. 6d. 



Lectures and Essays. By Professor Tyndall. (Watts <fe Co.) 6d. 

 The Insect Folk. By Margaret Warner ilorley. (Ginn & Co.) 2s. 

 Higher Criticism as Applied to Itself. By Artemus Longsides, 

 M.A. (Authors and Booksellers Co-operative Alliance, Limited.) Is. 

 Radiant Energy and its Analysis. Illustrated. By Edgar L. 

 Larkin. (Baumgardt Publishing Company.) 



Astronomy for Everybody. By Simon Newcomb, ll.d. (Isbister 

 & Co.) 7s.'6d. 



A Naturalist's Calendar. By Leonard Blomifield. Edited by 

 Francis Darwin. (C. J. Clay & Sons.) 



The Popish Plot and its Newest Historian. Bv the Rev. John 

 Gerard, s.j. (Longman, Green & Co.) Gd. 



The Reliquary. By J. Eomilly Allen, f.s.a. (Bemrose & Sons, 

 Limited.) 2s. 6d. 



The Burlington Magazine. No. 5. (Savile Publishing Co.) 2s. 6d. 

 Nur.ies and Nursing, or How not to do it. By Sister Medicatrix, 

 Ex -N.S. (The Authors and Booksellers Co-operative Alliance, 

 Limited.) 6d. 



Booklet on Goerz Trieder Binoculars. C. P. Goerz. Free. 

 Water and Air, or New Thoughts on Old Subjects. By J. P. 

 Sandilands, ma., t.c.d. (The Authors and BookseUers Co-operative 

 Alliance, Limited.) 4d. 



Das Zeissuerk und du Carl-Zeiss-Stiftang in Jena. By Felix 

 Auerbash. (Gustav Fischer.) 



List of Second-Hand Instruments. C. Baker. Free. 

 Urban Film Subjects. The Charles Urban Trading Co. Free. 

 Quacks and What they do. By One of Them. (Authors and 

 Booksellers Co-operative Alliance, Limited.) b'd. 



The Wellcome Physiological Research Laboratories. (Walter 

 Dovvson, Director.) 



Geological Rambles in East Yorkshire. By Thomas Sheppard, 

 F. G.s. (A. Brown & Sons, Limited.) 



