732 



NATURE 



[February 3, 1921 



1906 at the instance of Sir S. Eardley Wilmot, 

 provision was made for res"earch work in sylvi- 

 culture, forest botany, zoology, and chemistry, 

 as well as in forest economic products. A scheme 

 now under consideration contemplates a large in- 

 crease in the establishment and equipment of 

 this institute, involving the acquisition of a 

 site of 1000 acres and an expenditure of some 

 50o,oooZ. 



It is interesting to note that, as the work of 

 the Forest Department has increased in volume and 

 complexity, the organisation which sufficed when 

 forest work was relatively simple and of a routine 

 nature has proved to be no longer suitable, and 

 in recent years there has been a considerable 

 advance in the direction of decentralisation. Thus 

 the major provinces now have complete control 

 over their forest revenue and expenditure, while 

 the provincial chief conservators carry out many 

 of the duties which previously were performed by 

 the head of the department. Similarly, it is now 

 recognised that a great deal of research in sylvi- 

 culture and economic products must be carried out 

 by local officers in the provinces, and not by the 

 staff of the Central Research Institute at Dehra 

 Dun. At the same time, the value of the assist- 

 ance and advice which can be obtained from 

 officers who are given opportunities of studying 



those aspects of problems which are usually not 

 accessible to local provincial officers is fully 

 realised. The Forest Department, in this respect, 

 appears to have realised from actual experience 

 the importance of (i) freedom for the develop- 

 ment of local initiative, and (2) mutual good-will, 

 which renders possible loyal co-operation and co- 

 ordination of work for the common good — prin- 

 ciples which, after all, constitute the foundation 

 of the British F^mpire itself. 



In a recent publication issued by the Govern- 

 ment of India it is noted that the Indian forest 

 estate constitutes a "huge mine of wealth, the 

 fringe of which has been barely touched," and 

 whether regarded from the commercial or the 

 scientific point of view the magnitude and many- 

 sided interest of the work which lies before the 

 officers of the Indian Forest Department to-day 

 can scarcely be surpassed. Finally, the forest 

 officer in India who is brought into intimate con- 

 tact with men of all degrees, ranging from the 

 aboriginal tribes of remote forest tracts to cap- 

 tains of industry and scientific experts, has it in 

 his power to do much to promote the good-will and 

 co-operation between men of different classes, 

 occupations, races, and creeds which are so im- 

 portant to-day for the welfare of the British 

 Fmpire and, indeed, of civilisation itself. 



The Investigation of Gravity at Sea. 

 By Prof. W. G. Duffield. 



T^HE most notable attempt to measure the varia- 

 -'- tion of the force of gravity over the surface 

 of the oceans was that made by Hecker in the 

 early years of the present century; in igoi he 

 surveyed a track across the Atlantic from Lisbon 

 to Bahia, following this up a few years later with 

 the investigation of the Indian and Pacific Oceans 

 and the Black Sea. 



Helmert had developed a formula for the varia- 

 tion of gravity with latitude from observations 

 collected from a large number of land stations, 

 and the immediate object of Hecker's investiga- 

 tion was to test its application to determinations 

 made over great ocean depths. The problem of 

 an oceanographic gravity survey has long fascin- 

 ated geophysicists, because observations on board 

 ship are practically made from the surface of the 

 geoid, and should lead to the determination 

 of the shape of that much-discussed figure ; and 

 what is also of importance, its solution should 

 likewise lead to a knowledge of the extent to which 

 isostatic compensation is complete over otherwise 

 inaccessible parts of the globe. 



Since observations of gravity must be made 

 with great accuracy if they are to be of any value 

 for such purposes, the examination of the gravita- 

 tional acceleration at sea is attended by great diffi- 

 culties ; on a moving ship, rolling and pitching pro- 

 duce vertical accelerations which are individually 

 indistinguishable from deviations from the true 

 value of g. Reliance must therefore be placed 

 upon suitable damping devices which will reduce 

 NO. 2675, VOL. 106] 



the effect upon the instruments of such extraneous 

 accelerations, or at least enable their mean value 

 to be determined within narrow limits of error. 



Hecker's original method depended upon the 

 simultaneous measurement of the atmospheric 

 pressure by means of a mercury barometer and a 

 boiling-point apparatus ; the latter determination 

 is independent of the local value of gravity, and, 

 if equated to pgh for the mercury column, gives 

 the necessary information for the evaluation of 

 g. A fine constriction in the barometer tube 

 provided a heavy damping factor which reduced 

 the amplitude of the oscillations of the mercury 

 surface; some of Hecker's instruments recorded 

 photographically upon a moving film and provided 

 a trace from which the normal level of the mercury 

 might under favourable conditions be gauged. 



Hecker considered that his observations showed 

 that Helmert's formula held good within, roughly, 

 one part in 30,000 for both deep and shallow seas, 

 indicating a high degree of isostatic compensa- 

 tion ; his conclusions have, however, been subjecv 

 to a good deal of unfavourable criticism both on 

 this and on the other side of the Atlantic, and it is 

 true that disappointing inconsistencies appear in 

 successive boiling-point determinations and in the 

 simultaneous readings of the four barometers, 

 which possessed different amounts of "lag," and 

 that in certain other respects objections may be 

 urged which prevent us from accepting the verdict 

 on the evidence placed before us ; nevertheless, 

 it was pioneering work, and the diflTiculties to be 



