November i8, 1920] 



NATURE 



369 



of wave-motion and vortex-motion. Both water- 

 and sound-waves are discussed, including the 

 change of form of progressive waves on water. 

 The analogies with other branches of science are 

 pointed out from time to time, such as, for ex- 

 ample, that between the magnetic field of an elec- 

 tric current and the irrotational motion round a 

 vortex filament. The book should be valuable both 

 to readers approaching electricity and hydro- 

 dynamics for the first time, and to those who have 

 studied either alone in detail. S. C. 



The Surveyor's Art. 



Geodesy: Including Astronomical Observations, 

 Gravity Measurements, and Method of Least 

 Squares. By Prof. G. L. Hosmcr. Pp. xi + 368. 

 (New York : John AV'iley and Sons, Inc. ; 

 London : Chapman and Hall, Ltd., 1919.) Price 

 i8s. 6d. net. 



PROF. HOSMER'S text-books on surveying and 

 allied subjects are well known, and any 

 further contribution from his pen is sure of a 

 welcome from all those either actually engaged 

 upon, or interested in, the art of mapping the 

 earth. We here use the word "mapping" in its 

 complete sense — namely, as including everything 

 requisite to the most minute delineation of the 

 earth's surface, and of such physical quantities 

 dependent upon its interior constitution as can 

 be determined by surface observations. 



The present book, based upon the practice and 

 researches of the United States Coast and Geo- 

 flotic Survey, is designed as a text-book for 

 ■students of the higher branches of the art. We 



in only lament that no such volume has yet 

 ippeared based upon British surveying practice, 

 .1 deficiency due partly to the fact that the great 

 survey work of a geodetic character recently 

 in progress in the British Empire has been that 

 <arried out by the Indian Survey Department, 

 a body which has always trained its own staff 

 and never summarised its methods in a text- 

 lxK)k, and partly to the complete non-existence of 

 any sch(K)l of geodesy in this country. Should 

 such a school ever be established, and should we 

 ever riTognis<! that, taking the lowest point of 

 view, it would pay us to put the sur\'ey of our 

 \frican territories upon a scientific and permanent 

 liasis, and to discontinue the present fragmentary, 

 liaphazard, and unscientific methods, the experi- 

 ence gained by the I'nited Stales Coast and 

 'leodetic Survey, the sy.stem it has e\-olvcd, 

 ind the body of practice it has formulated 

 will bo worthy of the closest stud-.. On 

 NO. 2664, VOL. 106] 



some points of detail surveyors trained in 

 other countries would doubtless depart from 

 the .\merican practice, while the latter would, 

 in other points, possibly require supplementing ; 

 there has been, for example, little occasion to 

 develop any procedure specially applicable to very 

 dense forest country ; but on the whole the ex- 

 perience and skill of the American surveyors may 

 be safely taken as guides for any future work. 



We do not quite follow Prof. Hosmer in his 

 apparent support of the now rather out-of-date 

 search for the " figure of the earth " in the form 

 of the spheroid which most closely fits the true 

 surface. For convenience of calculation some 

 spheroid must be assumed, but, provided that this 

 is approximately true, such an approximation as 

 is furnished by any of the well-known figures, 

 the exact spheroid selected is unimportant. The 

 shape of the geoid, the ultimate objective of the 

 surveyor, can be as well represented in relation 

 to one spheroid as to another. Great practical 

 convenience, however, accrues if all survey 

 systems — in any case those which have, or pos- 

 sibly could have in the future, a land connection 

 — are reduced to the same conventional figure. 

 All the North American surveys from Canada to 

 Mexico have now adopted the Clarke (1866) figure 

 and no further knowledge of the earth's true 

 shape will compel them to abandon this as the 

 basis for their reductions. 



As regards the system of levels we are doubtful 

 whether the convention adopted in the United 

 States of applying an orthometric correction and 

 thus defining level so that two points on an 

 undisturbed lake are at different levels is, on the 

 whole, the best. We should prefer to treat 

 any points on the same equipotential surface 

 as being at the same level, and re-define 

 height to mean the distance of the equipotential 

 from the geoid at a selected latitude. This is a 

 subject which might with propriety engage the 

 attention of the International Geodetic Congress 

 when that bodv is summoned. E. H. H. 



Ronald Poulton. 



The IJfe of Ronald Poulton. By his I'allKT, 

 Edward Bagnall Poulton. Pp. xi + 410. (l-on- 

 don : Sidgwick and Jackson, Ltd., 1919.) Price 

 i6i. net. 



NOT only thos« who were the intimate com- 

 panions of Ronald Poulton, but likewise the 

 rest — and they were legion- -who admiringly wit- 

 nessed his deeds of prowess in the field, were able 

 to realise that behind all the brilliant qualities of 



