July 2 1, 1881] 



NATURE 



259 



" That volcanoes are thus built up along lines of fissure 

 in the earth's crust, we have the most convincing proofs. 

 Not only have such fissures been seen in actual course of 

 formation at Vesuvius, Etna, and other active volcanoes, 

 but a study of the volcanoes dissected by denudation 

 affords the most convincing evidence of the same fact. 

 The remarkable linear arrangement of volcanoes, which 

 is conspicuous to the most superficial observer, is a very 

 striking evidence of the same fact." A slight looseness 

 of expression is also apparent when the author speaks of 

 carbonic acid as a poisonous gas, the fact being that the 

 gas produces suffocation by spasmodically closing the 

 glottis and without entering the lungs at all. On the 

 other hand, carbonic oxide, which has a direct and baneful 

 action on the organism, may truly be described as a 

 poisonous gas. 



In the account of Geysers the author, after stating that 

 many attempts have been made to explain the mechanism 

 by which the intermittent action of geysers is produced, 

 remarks that probably no " such explanation will cover all 

 the varied phenomena exhibited by them." Herein he 

 does not even allude to Bunsen's classical experiments on 

 the action of geysers, which are generally accepted as 

 furnishing conclusive proofs of the mechanics of these 

 intermittent springs. 



A highly-instructive chapter discusses the number and 

 distribution of volcanoes. In the second edition the map 

 inserted at the beginning of Mr. Scrope's book might 

 with advantage be introduced. 



Concluding chapters discuss the information furnished 

 by volcanoes concerning the interior of the earth, and the 

 attempts made to explain the causes of volcanic action. 

 In regard to this latter matter we are left as much in the 

 dark as ever, and authors usually content themselves with 

 stating the various hypotheses which have been proposed, 

 leaving the reader to select that which he considers the 

 most rational. 



Prof. Judd's work is very instructive, and it will excite 

 intense interest in the minds of many readers. Laid down 

 upon the lines of Mr. Scrope's book, it is less methodical, 

 less philosophical, and to most people more readable. A 

 few things seem to us to be wanting, but probably the 

 author has good reasons for their omission. Particularly 

 we notice the absence of references to the labours of such 

 men as Bunsen, von Waltershausen, Johnstrup, von 

 Lasaulx, Steenstrup, Elie de Beaumont, and Tacchini. 

 Iceland, the most marvellous country in the world from 

 the volcanic point of view, is scarcely alluded to. And. 

 as we said above, it seems to us that we require some 

 vovi to arrange and put in order the countless ofioio/xtpfiai 

 that are scattered throughout the pages. But even with- 

 out this we cannot read the book attentively without 

 feeling that we have acquired a great mass of information 

 concerning phenomena which have occupied the attention 

 of wise men from the earliest times. 



G. F. RODWELL 



THE FIGURE OF THE EARTH 



The Fii^tire of the Earth : an Introduction to Geodesy. 



By Mansfield Merriman. (New York, 1881.) 



THE author of this volume has already made his 

 name known to us as the writer of an excellent 

 treatise on the Method of Least Squares. The book 



before us presents to the reader, who is supposed to have 

 some little knowledge of Algebra and Geometry, an ex- 

 planatory and historical sketch of the labours of geodesists 

 from the earliest days. We read in Chapter I. that 

 Anaximander — a speculator in Geometry, Astronomy, and 

 other sciences — concluded, from some reasons best known 

 to himself, that the earth was a cylinder whose height is 

 three times its diameter. There must have been some 

 good reason for this idea, for we are told that Anaxa- 

 goras held the same. And it is scarcely to be wondered 

 at that Plato originated some views of his own in the 

 matter. 



Passing to comparatively modern times we have a de- 

 tailed account of the measurement of a degree (in 1766-68) 

 by Mason and Dixon along the boundary line between 

 the states of Maryland and Delaware. This measure gave 

 3947 miles as the radius of our supposed sphere. 



Then the Franco- Peruvian expedition — circa 1736 — of 

 the Academicians MM. Bouguer and Lacondamine is 

 briefly referred to (and here there is a misprint in the 

 length of the base-line at Cotchesqui, which was 6274 

 toises in length), their labours giving 3936 miles as the 

 radius. Henceforth the earth, abandoning its claims to 

 sphericity, and not escaping a temporary imputation of 

 being egg-shaped, settles down into an oblate spheroid — 

 the figure generated by the revolution of an ellipse round 

 its lesser axis. 



Chapter II. treats of the method of determining the 

 e.xcentricity of this spheroid. As one measured arc will 

 determine the radius of the spherical earth, so two 

 measured arcs determine the radii of the spheroidal earth, 

 that is, if the two arcs differ considerably in latitude. 

 The actual excentricity is then calculated from the arc 

 measured in Peru and that measured in Lapland. Then, 

 further, taking the arc measured in France and combining 

 these three in pairs, three quite different values of the ex- 

 centricity are obtained. Here enters a discord not yet 

 resolved ; and in fact all modern measurements show that 

 the earth is not a true spheroid, for, combining the arcs 

 in pairs, all kinds of values of the excentricity present 

 themselves. Then we fall back on the method of least 

 squares, and grouping all the measurements into a unique 

 calculation, we get a unique value of the excentricity, 

 which may, with some show of reason, be called the most 

 probable value. A specimen of this mode of calculation 

 applied to pendulum observations is given at page 52 ; 

 and it may be noted in passing that the calculation would 

 have been made both neater and simpler by writing 

 S -j- 39 instead of S. By inadvertence it is stated at page 

 54 that pendulum observations give I-288-5 as the earth's 

 ellipticity, and again at page 64, 1-289 >s given as the re- 

 sult of the same observations. But these are the ellipti- 

 cities that were obtained previous to the very extensive 

 pendulum work recently completed by General Walker in 

 India. When these modern observations are taken into 

 account the 1-289 is changed to 1-292 or 1-293. 



The earth then being no true spheroid, an attempt, 

 described in Chapter III., is made to ascertain whether 

 it is an ellipsoid with three unequal axes. Here but little 

 better success is met with, and failing to establish for 

 itself any fair name, the earth, like other pretenders, takes 

 shelter under hard words, and in the concluding chapter 

 of the book calls itself a geoid. Here we are safe and 



