626 



NATURE 



[January 13, 1921 



oil prospecting- of the more precise methods of 

 j^eological survey. Such work can be carried out 

 only by competent persons qualitied to undertake 

 a survey for oil, and this implies training of a 

 highly specialised character. Tho.se who have had 

 any experience, therefore, in this branch of teach- 

 ing will readily appreciate the value of a book 

 such as Mr. L. S. Panyity has written, a book 

 which must also make a wide appeal to the 

 student and to the oil geologist of the older school. 



Considered purely from the academic point of 

 view, the volume can unhesitatingly be put into 

 a student's hands at the outset of his course with- 

 out any apprehension as to its suitability as pre- 

 face to both lecture and practical work. From 

 the composition and origin of oil and gas, their 

 migration and accumulation, through all the in- 

 tricacies of modern methods of surveying and pros- 

 pecting, to the sinking of wells and the production 

 of crude oil, the author takes his reader through 

 a thorough course of elementary instruction with- 

 out burdening him with unnecessary technical 

 detail. The early chapters deal with general geo- 

 logical definitions, conventions, and successions, 

 considered from the point of view of oil technology. 

 From these we pass directly to actual field-work, 

 initiated by .a lucid exposition of plane-table 

 survey, including the more exact processes in 

 triangulation. In the succeeding chapters, deal- 

 ing with actual maps, it is pleasing to note that 

 the construction and reading of isobath and iso- 

 chore maps receive adequate attention, as both 

 these phases of the subject present difficulties to 

 the novice at first, though we should have pre- 

 ferred that the question of the interpretation ^of 

 geologic structures had received fuller discussion, 

 even to the exclusion (if necessary) of the long 

 chapter on fossil flora and fauna. Condensed 

 palaeontology or pala?obotany is seldom a success, 

 and with the great number of useful text-books 

 available for studying these subjects such an 

 omission would need no apology. 



The remaining pages of the volume are devoted 

 more to the engineering aspects of oil prospecting, 

 and include chapters on the location, sinking, 

 spacing, and completion of wells, together with 

 some notes on regulating the course of production 

 of the crude oil derived. A somewhat lengthy 

 appendix contains some useful tables of constants 

 for triangulation work, and also for calculating 

 the capacities of gas wells, etc. 



As is usual with American publications of this 

 nature, the book is profusely illustrated with maps 

 and diagrams, and the inevitable " Landscape and 

 Topographic Contour Map " (depicted on the in- 

 side cover of all the folios of the United States 

 Geological Survey) finds a place here on p. 70. It 

 NO. 2672, VOL. 106] 



is undoubtedly an attractive and useful publication, 

 which, by virtue of its clearness of diction, careful 

 arrangement of subject-matter, and freedom from 

 "padding," should make an appeal to a very wide 

 public. H. B. Mii.NEK. 



The Induction Coil of To day. 



Induction Coil Design. By M. A. Codd. 

 Pp. vi-i-239-fi4 plates. (London: E. and 

 F. N. Spon, Ltd., 1920.) Price 21s. net. 



IT is only within the last few years that the in- 

 duction coil has emerged from the sanctum of 

 the philosophical instrument maker and even ap- 

 proximated to an electrical engineering "job." It 

 cannot yet be said to have shaken itself free of 

 the trammels of empiricism, and it too often 

 serves largely as a medium for the skill of the 

 cabinet-maker and french polisher to impress a 

 susceptible clientele. Moreover, for X-ray work 

 at any rate (and in particular for work with thi 

 Coolidge tube), the interrupterless transformer i- 

 finding fresh adherents each day, and it was high 

 time that the case for the induction coil should be 

 put by one who is conversant with coil construe 

 tion and design. 



Mr. Codd candidly concedes at the outset that 

 precision measurements of coil phenomena are 

 difficult, if not impossible, and as a consequenct- 

 present-day design rests mainly on arbitrarv 

 standards which have been evolved empirically 

 from practical experience. Holding the view thai 

 a knowledge of these standards should not bf 

 confined to the coil-maker, Mr. Codd has accord- 

 ingly collected data from his experience of a 

 number of typical and accepted designs, and set 

 them out comparatively in the present book. To- 

 the coil-maker the wealth of practical and dia- 

 grammatic detail should be of value ; and even 

 the user, primarily concerned with performance, 

 will be interested to learn of the constructional 

 precautions and skill which have to be exercised, 

 and of the relative common-sense values of the 

 several designs on the market, for each of which 

 extravagant claims of super-efficiency have usually 

 been advanced by its author. 



Here it may be remarked that the efficiency 

 of even a large coil rarely reaches 50 per cent., 

 and is usually nearer 30 per cent. Nor can the 

 same coil be equally cflficient for all purposes. It 

 is in the success with which he reconciles an- 

 tagonistic factors that the coil-maker's art finds 

 its greatest expression. He knows, as a practical 

 fact, that for a given transformation ratio the 

 secondary winding should be such as to keep the 

 self-induction as low as possible ; he has found 



