284 Scientific Intelligence. 



spheroid had been in use by the Coast and Geodetic Survey for a 

 number of years but this was found to be quite far from the truth 

 after Clarke had carried on his investigations for the determina- 

 tion of the figure of the earth. After that the Coast and Geodetic 

 Survey adopted the Clarke spheroid of 1866 as its reference 

 spheroid and it is believed that this spheroid is so near the truth 

 that, for all scientific and geodetic purposes, it need never be 

 changed, in so far as the triangulation of the United States is 

 concerned. Undoubtedly the Helmert spheroid, which will be 

 adopted by the Trigonometric Survey of India, will meet the 

 needs of India for all time. 



Hunter has chapters in his book on the various phases of the 

 change of a triangulation system from one spheroid to another. 

 This includes an interesting statement on the adjustment of trian- 

 gulation and a chapter on the probable errors of triangulation 

 before and after adjustment. There are included in the publica- 

 tion data for the 108 gravity stations which had been established 

 in India prior to the appearance of this book. The data include 

 the gravity anomalies based on the three generally used methods 

 of reduction, namely, the free air, the Bouguer and the isostatic 

 hypotheses. These data, with regard to gravity stations, are 

 duplicates of the same material appearing in Professional Paper 

 No. 15, of the Trigonometrical Survey of India. 



The last chapter of the book contains a discussion of the data 

 relative to deflections of the plumb line and the values of the 

 intensity of gravity at stations established in Turkestan by Rus- 

 sian observers. It is interesting to note on the chart which accom- 

 panies the report the relation of the deflections of the vertical to 

 the topography of the area covered by the stations and to their 

 north and south. There is a station close to the southern margin 

 of the valley near the foot of high mountains with a deflection to 

 the southward of 49".4. To the north of the valley and just to 

 the south of a range of mountains is a station with a deflection of 

 the vertical to the northward of 26". 9. The relative station error 

 between these two stations is 76".3, while their difference in lati- 

 tude is only about 65 miles. This is quite a remarkable case and 

 shows the impossibility of having only astronomic observations 

 for the control of surveys and maps. If surveys had been made 

 and maps based on each of these astronomic stations, when the 

 two surveys were joined there would be an overlap, in position, 

 on the resulting maps of about 1% miles. This is one of the 

 strong arguments in favor of having an area covered by con- 

 tinuous triangulation, as has been done in most of the countries of 

 the world. 



The gravity anomalies shown on the Turkestan map have not 

 been reduced by the isostatic method. It is hoped that this may 

 be accomplished at an early date for there has always been great 

 interest attached to the condition of isostasy in Asia, outside of 

 India where much data are available, and here is an opportunity 

 of throwing some light on this important question, w. B. 



