146 



NA TURE 



\_Dec. 13, if 



former subject at least, Stokes stands, without a living 

 rival, the great authority. From the Aberration of Light, 

 the Constitution of the Liinii)iiferous Ether, the full ex- 

 planation of the singular difficulties presented by A'cwton's 

 Rings, to the grand theoretical and experimental treatise 

 on the Dynamical Theory of Diffraction, we have a series 

 of contributions to this branch of optics which, even 

 allowing for improved modern surroundings, will bear 

 comparison with the very best work of Newton, Huyghens, 

 Young, or Fresnel in the same department. 



Specially remarkable among the Hydrodynamical 

 papers is that on Oscillatory IVavcs, to which a very 

 important addition has been made in the reprint. The 

 investigation of the "profile" of such a wave is here 

 carried to a degree of approximation never before 

 attempted. 



Besides these classes of papers we have the very valu- 

 able treatise on Friction of Fluids in Motion, and on (he 

 Equilibriiun a?id Motion of Elastic Solids. This was 

 Stokes' early masterpiece, and it may truly be said to 

 have revolutionized our knowledge on the subjects it 

 treats. To mention only one point, though an e.xceed- 

 ingly important one, it was here that for the first time 

 was clearly shoivn the error of assuming any necessary 

 relation between the rigidity and the compressibility of 

 an elastic solid, such as had been arrived at from various 

 points of view by the great Continental mathematicians of 

 the earlier part of the present century. 



Of the few purely mathematical papers in the present 

 volumes the most important is the well-known examina- 

 tion of the Critical Values 'of the Sums of Periodic Series, 

 a subject constantly forced on the physicist whenever he 

 has to treat a case of discontinuity. 



We need not say that the printing of these volumes is 

 all that could be desired : the name of the Pitt Press is a 

 sufficient guarantee. But the introduction, for the first 

 time, of a solidus to save " spacing " and space in the 

 printing of mathematical formute, was a bold step on the 

 part of Prof Stokes : — since amply justified by the testi- 

 mony of the readers of the first of these volumes, and 

 still more by its almost immediate adoption by thoroughly 

 scientific as well as practical men, such as the Editors of 

 what we still feel inclined to call by the well-known name 

 oi Pogge?idorff's Aiinalen. P. G. Tait 



ROYAL ENGINEER PROFESSIONAL PAPERS 

 Professional Papers of the Corps of Royal Enoineers. 

 Edited by Major R. H. Vetch, R.E. Vol. VIII. 1882, 

 214 pp., 39 pi. (London : Stanford, 1883.) 



SO many essays were contributed to these papers in 

 1882 that it was found necessary to publish two 

 volumes for that year. This is a healthy sign of the in. 

 terest taken by the Corps as a whole in their profession. 

 Vol. VII. was devoted entirely to permanent fortification, 

 a purely professional subject; whilst Vol. VIII. contains 

 eleven papers, several of which are of general interest. 

 This volume must have been an expensive one to get up, 

 as it contains thirty-nine plates, some of them pretty 

 large : the size and expense of the volume might have 

 been considerably reduced if the contributors had pre ■ 

 pared their plates in a more convenient shape ; e.g. one 



plate, a mere genealogical table, and not really a large 

 one (Appendix I.), has eight cross folds and one longitu- 

 dinal one ; this could easily have been much compressed. 



Paper 3 is a careful and well got up study of the " Cam- 

 paigns of Lord Lake against the iMarattas," 1804-6 (92 pp., 

 with nine plates), which will be read with interest by all 

 students of military campaigns. A good illustration of 

 the difficulty of ascertaining the truth about events of 

 eighty years back occurs in the verification of the site of 

 the "battle of Delhi" (1803) ; the supposed site is actu- 

 ally marked by a pillar with inscription ; but, after care- 

 ful collation of contemporary surveys and reports of 

 marches, the author decides against the site marked by 

 the pillar. 



Paper 8 is an interesting account of the " Triangula- 

 tion of Northern Afghanistan" carried out during the 

 late war. It is worth notice here that the introduction of 

 the heliograph into army signalling has thrown a difficulty 

 in the way of the use of the heliotrope for survey (in the 

 field), from the liability of confusing the signals ; but 

 there seems little doubt that in the future the army helio- 

 graph stations could be used for the survey, and be an 

 assistance instead of a hindrance to the survey. The 

 general result of the altitude observations has been to 

 throw doubt on the efficiency of the aneroid, a result 

 much to be regretted. The refraction, which in India is 

 about '067 of the contained arc, was found to amount to 

 "08 of the same in the Afghan hills ; an unusual result, as 

 refraction commonly decreases with altitude. 



An interesting paper (No. 9), on " Organic Compounds 

 in the Sun," by Capt. Abney (read in 1881), gives a 

 popular r«/c;«e' of the subject (up to 1881), ending with 

 the author's spectroscopic researches showing the pre- 

 sence of hydrocarbons in the sun and probably in space 

 itself ; this last raises curious questions as to the consti- 

 tution of the ether ; can space be really full of hydro- 

 carjjons ? This paper has suffered rather by the delay in 

 publication. 



Perhaps the most important (military) paper is No. 10, 

 on " Railways for Military Communications in the Field." 

 The author shows that the early attempts at introducing 

 railways on field service all failed to be of much practical 

 use from their unsuitability to the conditions, the first of 

 which is lightness and portability of both rails and 

 rolHng-stock, and it is just herein that the English rail- 

 ways fail most, being amongst the heaviest in the world. 

 A light railway largely used in the United States, which 

 has been laid at the rate of four miles a day, is favourably 

 mentioned. After recapitulating the various schemes 

 which have been tried or proposed, the author gives his 

 conclusions as to the conditions for a military railway; 

 among the most important of these are that the gauge 

 should be 2| feet, the rails lolbs. per foot, and the line 

 double. It is clearly impossible for any country to keep 

 a large stock of railway plant specially for service : now 

 it so happens that this 2i-foot gauge is already in use to 

 some extent in Europe, so that the requisite plant could 

 probably be obtained at short notice in Europe. In 

 India, however, the metre-gauge is so largely in use that 

 field railways in or near India will jirobably for many 

 years perforce be of metre-gauge. The field railway laid 

 for the use of the British army in South Afgahnistan(i879- 

 80) is not mentioned ; this railway was laid for a great 



