66o SCIENCE PROGRESS 



omission, as it is undoubted that their employment by survey parties will 

 soon become general, much time spent in observation and computation being 

 saved. 



One chapter is devoted to the properties of the spheroid, and the methods 

 of calculation of triangulation and geodetic positions are dealt with. The 

 problem of the adjustment of triangulation is dealt with in some detail, and 

 is preceded by a brief account of the method of least squares. This is based 

 upon the probability aspect and is clear and concise, though the proof of the 

 error law is not rigid. It may be noted that there is an error in the second 

 of equations (147), for v^ in the denominators of the differentials should be 

 read z^ ; in addition, the right-hand sides of the equations have been omitted. 



The chapter on map projections is the least satisfactory one in the book. 

 The fundamental principles of projection are not clearly brought out, nor 

 are the relative advantages of the several projections which are dealt with 

 sufficiently explained. The chapter as it stands would not enlighten very 

 much a student approaching the subject for the first time. 



At the end of the volume is given a series of formulae, numerical constants, 

 and tables which will prove valuable for reference purposes. 



H. S. J. 



The Gyroscopic Compass. A Non-mathematical Treatment. By T. W. 



Chalmers, B.Sc, A.M.I.Mech.E. [Pp. x + 167, with 51 figures.] 

 (London : Constable & Co. Price lis. net.) 



The contents of this book originally appeared as a series of articles in 

 The Engineer in the early part of 1920. The articles were intended to give a 

 clear account of the theory and construction of the gyroscopic compass, 

 without the introduction of mathematics. The author has succeeded 

 admirably, and the volume is a model of how an abstruse and difficult subject 

 can be treated in an elementary manner without loss of accuracy or ignoring 

 difficult points. 



The gyro-compass has become a necessity on the modem battleship, 

 owing to the difficulty of ensuring that a magnetic compass will be unaffected 

 by the large masses of iron and steel around it. The three existing patterns 

 of gyro-compass — the German Anschiitz, the American Sperry, and the British 

 Brown compass — were developed primarily for naval purposes. The 

 gyro-compass is, however, certain to have a large future before it in the 

 mercantile narine. The initial cost is somewhat heavy, but in the Preface 

 to this volume it is stated that " remarkable figures were shown to the author 

 recently which demonstrated that not only was navigation by the gyro- 

 compass much more accurate than by the magnetic compass, but that the 

 increased accuracy reduced the length of the voyage of a mercantile vessel 

 to an extent that resulted in saving a quantity of fuel, the value of which on a 

 single trip would go a considerable way towards meeting the extra first cost 

 of a gyro-compass." This book will help the navigating officer to understand 

 the principles upon which this type of compass is based. 



The treatment throughout is sufficiently detailed for easy reading. The 

 phenomena of the gyroscope and their application in the gjTo-compass are 

 described. The several errors to which the compass is liable (latitude error, 

 north steaming error, balUstic reflection, and quadrantal error) are fully dealt 

 with, and the manner in which they are eliminated in the three types of 

 compass is explained. The principal features of the three patterns and the 

 methods of damping the vibrations and eliminating fiction are described. 



There was no detailed account previously available dealing with the 

 gyro-compass in an elementary, non-mathematical manner, and the present 

 volume is for this reason the more welcome. It should do much to remove 

 the unjustifiable prejudice which exists in some quarters against the gyro- 

 compass. H. S. J. 



