14^ 



NA TURE 



[June 14, 1906 



more than six years since the second supplement 

 appeared, and in the interval the study of the kathode 

 stream, the phenomena of radio-activity, and in general 

 of everything concerned with the propagation of elec- 

 tricity in gases has given rise to a new conception 

 of electrical conductivity, and of the ultimate con- 

 stitution of what were once called the " electrical 

 fluids." The faith of scientific men in the non-trans- 

 mutability of matter has been shaken ; even the notion 

 of material mass tends to be absorbed in that of 

 electromagnetic inertia. 



This is the state of things as set forth in the pre- 

 face to this supplement ; no surprise need be felt, then, 

 at its large size compared with that of the preceding 

 numbers. The portion dealing with radiations in- 

 cludes amongst other things an account of recent 

 work on the energy of a block body, the pressure 

 of radiation, the laws of dispersion (normal and 

 anomalous), remainder rays, and N-rays. In regard 

 to the last-named subject, we have no wish to be dog- 

 matic; there is certainly some evidence that M. 

 Blondlot has been experimenting with objective, and 

 not entirely with subjective, phenomena, and if this 

 is so, experiments should not cease until the exact 

 nature of these phenomena has been established. But 

 when M. Bouty devotes nearly two pages to this sub- 

 ject, and does not even hint that there is doubt, 

 amounting to disbelief, in the minds of most of the 

 leading physicists of the world in regard to this 

 matter, we think that he is hardly doing justice to it. 



In electricity, leading sections deal with wireless 

 telegraphy, polyphase currents, the ionic theory, and 

 the work of Nernst. Under the head of ionisation 

 are taken the phenomena of ionisation in gases and 

 radio-activity. The volume concludes with some mis- 

 cellaneous practical applications of electricity. 



Any who are familiar with the main treatise and 

 the previous appendices will know that M. Bouty is 

 a master of lucid exposition ; there is no need to com- 

 mend this volume to them. Those who are desirous 

 of learning, in brief but clear summary, the present 

 state of knowledge in regard to the above supremely 

 important subjects may be recommended to read this 

 appendix. 



(3) The third of the above books is the first volume 

 of a course of elementary physics based on lectures 

 delivered to classes consisting largely of medical 

 students. As the reader is assumed to be attending 

 experimental lectures and, if possible, performing ex- 

 perimental work himself in a laboratory, small space 

 is given here to descriptions of experiments and of 

 methods of observation. 



The subjects dealt with are mechanics, and the pro- 

 perties of bodies in the solid, liquid, and gaseous 

 states. The sixth chapter consists of thermodynamical 

 considerations in respect to gases. This chapter is 

 undoubtedly very lucid, but we think that its proper 

 place is later on — after calorimetry. The mathematics 

 employed is simple, and the treatment very clear. The 

 name of the author is, of course, a sufficient guar- 

 antee of the nature of the book. We look forward 

 to seeing the German translation of the remainder. 

 NO. 191 I, VOL. 74] 



REDUCTION OF GEODETIC MEASURES. 

 The Adjustment of Observations by the Method of 

 Least Squares, with Applications to Geodetic Work. 

 By T. VV. Wright, with the cooperation of J. F. 

 Hajrford. Second edition. (New York : D. Van 

 Nostrand Co. ; London : A. Constable and Co., Ltd., 

 1906.) Price 3 dollars net, or 12s. 6d. net. 



THIS is a book which in its original form grew out of 

 the experience and requirements of the U.S. Coast 

 and Geodetic Survey. As points of novelty or diffi- 

 culty arose in the course of the work and were solved 

 by the staff, Mr. Wright collected the decisions and 

 the methods as guides for the treatment of similar 

 cases in the future. The systematic arrangement of 

 these cases, and the discussion of the principles which 

 furnished the solution, provided a mass of materia 

 which has been of great service to the department 

 An opportunity has now arisen for the revision o. 

 this work, and in the belief that the information 

 would be of advantage in many operations connected 

 with scientific engineering, the original author, in 

 collaboration with Mr. J. F. Hayford, chief of the 

 computing division and inspector of geodetic work, 

 has given to this material the form of a treatise. 



The book is eminently practical. The authors do 

 not enter into the question whether the principle of 

 least squares suggests the best or the only method 

 for deriving from a mass of imperfect data a result 

 that will command general confidence. They recog- 

 nise the fact that the method has secured an im- 

 pregnable place in all inquiries to which it is ap- 

 plicable, and proceed at once to discuss the law of 

 error on the ordinary Gauss-Chauvenet lines. The 

 subject necessarily does not lend itself to any novelty 

 of treatment. The value of the earlier chapters at 

 least lies in the fact that the authors place -before 

 us the results of a wide and profound experience. 

 Everywhere they keep in sight the practical treatment, 

 insisting on the importance of arithmetical checks 

 and processes of abbreviation. In this connection one 

 is glad to see DooHttle's system of solution set out 

 in a complete scheme, as well as other processes which 

 have a practical application. 



The question of the rejection of discordant observ- 

 ations will always occasion a computer some anxiety 

 The authors have evidently suffered, and the practical 

 rule given here may not be generally accepted, but 

 is valuable as showing, presumably, what is the prac- 

 tice in the U.S. Geodetic Survey. The authors advise 

 that no observation should be retained for which the 

 residual exceeds five times the probable error of a 

 single observation, and that all observations the re- 

 siduals of which exceed three and a half times the pro- 

 bable error of a single observation should be examined, 

 and rejected, if any of the conditions under which the 

 observation was made were such as to produce any 

 lack of confidence. The conviction is also expressed 

 that an observer's best observations are poorer than 

 he believes them to be, and his poorest better. As 

 a consequence of this the range of weights that ob- 

 servers attach to their observations is too large. 



Actual geodetic measures necessarily introduce the 



