240 Notices respecting Neiv Boohs. 



have been too enormous. The natural thing to attempt was to 

 determine differential corrections to the coordinates of each point. 

 This is the problem which Mr. Hunter has attempted and suc- 

 cessfully solved, and the volume under review contains the results 

 of his labours which have extended over several years, together 

 with much other interesting matter arising directly out of, or 

 suggested by, this research. 



The problem is not such an easy one as it might appear. The 

 complication arises from the fact that the observations have been 

 adjusted to fit the Everest Spheroid, and consequently will not 

 fit any other spheroid without readjustment. As a result of 

 this, the corrections obtained for the coordinates of any point 

 depend upon the route by which that point is reached from the 

 origin. Various routes are discussed in the memoir, and after a 

 detailed discussion it is concluded that, in view of the methods 

 by which the observations of the triangulation in Jndia have been 

 reduced, the method of calculation along geodesies through the 

 origin is the correct one to use. The discussion is of considerable 

 theoretical importance and the conclusion arrived at appears to be 

 justified. 



In the latter part of the volume the general questions of the 

 adjustment of a triangulation and of its "strength" are discussed.. 

 A criterion of the strength of a triangulation is determined which 

 is superior to General Eerrero's in that it takes account of the 

 length of the sides and the general formation of the series. This 

 quantity enables probable errors of length of side and azimuth 

 and also of latitude and longitude of any point of the triangulation 

 to be expressed. Numerical values of the strength of all the 

 Indian series of triangulation are given. The more difficult 

 question of the assignment of probable errors after adjustment is 

 considered in some detail. 



An interesting by-product of the investigation is a pretty 

 method for the solution of a large number of normal equations 

 in the particular case when the equations can be divided into 

 groups in each of which certain of the variables have zero co- 

 efficients. A well-ordered method of solution is illustrated in 

 detail by a numerical example. 



The volume embodies the results of a long and laborious research,, 

 and the results obtained are of the greatest practical importance. 

 The author and the Survey of India are to be congratulated 

 upon it. H. S. J. 



