426 Geological Society : — 



which Prof. Plummer relies on analytical methods may be gauged 

 by the fact that there are only eight diagrams in the book. We need 

 not dwell further on these minor points in which we happen to 

 take a different view from the author; but rather would hasten 

 to express our gratitude to him for a book which we have placed 

 on the shelf reserved for those in most constant use. 



A subject on which so many of the great mathematicians of the last 

 century have laboured tends to take a stereotyped form; but the 

 author has succeeded in introducing much freshness of treatment, 

 and he dispels any impression that the subject is played out. Many 

 results are included that are not readily found elsewhere ; and 

 good use is made both of modern researches and half-forgotten 

 results of the past. The account of the determination of spectro- 

 scopic orbits meets a need of recent growth. The collection of 

 interpolation and numerical integration formulae in Chapter XXIV. 

 is the best we have seen, though we miss our own particular 

 favourite (the quadrature formula of Darwin, ' Collected Papers,' 

 vol. iv. p. 17), which has yet to find a place in any textbook. 



The writing of this treatise must' have cost a vast amount of 

 labour, and we congratulate Prof. Plummer on a most successful 

 result, which should aid and stimulate the study of dynamical 

 astronomy in this country. 



XL VIII. Proceedings of Learned Societies. 

 GEOLOGICAL SOCIETY. 

 [Continued from p. 364. J 



May 1st, 1918.— Mr. GL W. Lamplugh, E.R.S., President, 

 in the Chair. 



Dr. A. Hubert Cox, M.Sc, F.G-.S., delivered a Lecture on the 

 Relationship between G-eological Structure and Mag- 

 netic Disturbance, with especial reference to Leicestershire 

 and the Concealed Coalfield of Nottinghamshire. 



Before the Lecture, at the request of the President, Dr. A. 

 Strahan, F.R.S., Director of the Geological Survey, briefly out- 

 lined the circumstances that had led to an investigation into a 

 possible connexion between geological structure and magnetic dis- 

 turbances. The magnetic surveys conducted by Riickerand Thorpe 

 in 1886 and 1891 had proved the existence of certain lines and centres 

 of disturbance, but those authors observed that 'the magnetic 

 indications appear to be quite independent of the disposition of the 

 newer strata,' and he (the speaker) had not been able to detect any 

 obvious connexion with the form and structure of the Palaeozoic 

 rocks below. In 1914-15 a new magnetic survey was made by 

 Mr. G-. W. Walker, who confirmed the existence of certain areas of 

 disturbance. It was suggested that the effects might be due to 

 concealed masses of iron-ore, and the matter was referred to the 

 Conjoint Board of Scientific Societies, who appointed an Iron -Ores 

 Committee to consider what further steps should be taken. The 

 Committee recommended that attention should be concentrated 

 on certain areas of marked magnetic disturbance, and that a more 



