NATURE 



[December 30, 1909 



THE SLRVEV OF INDIAA 



THE report on the operations of the Survey of India 

 for the year 1907-8, in addition to the usual 

 record of map-maliing of a utilitarian character, con- 

 tains several features of scientific interest. We have 

 long been accustomed to a high standard of work from 

 this department, and it cannot be other than a subject 

 of congratulation that we should see evidence, not 

 only of the maintenance of its previous level, but also 

 fif continuous advance. The most recently completed 

 geodetic triangulation, extending for a distance of 

 4S0 miles from the Indus to the peak Koh-i-Malik 

 Siah, the junction point of India, Persia, and Afghan- 

 istan, is the most accurate operation of its class ever 

 carried out in any country. Computed by the ordinary 

 methods, the probable error of a single angle is o"'2i, 

 a quantity not much more than half that of the corre- 

 sponding figure obtained in any triangulation outside 

 India. 



This series of triangles carries the geodetic work to 

 a point marking the most westerly limit reached by 

 the principal triangulation of India. At this distance 

 from the centre of the network the errors of the 

 .issumed spheroid become noticeable. Thus the astro- 

 nomical azimuths observed along this line arc con- 

 sistently smaller than the azimuths computed from the 

 triangulation, showing that the computation is taking 

 the points too far to the north, i.e. that the curvature 

 of the spheroid used for the reductions is, over this 

 region, appreciably greater than that of the true 

 geoid. 



Pendulum operations were carried on during tlie 

 year with the special object of ascertaining whether 

 the force of gravity would be found in defect in sub- 

 montane tracts in the south of India to the same 

 degree as in the Himalayan region. In all cases the 

 dcliciency was found to be considerably less at these 

 stations than at places of similar altitude in the 

 north. It was also found that for stations on "iso- 

 lated " hill-masses the degree of compensation of the 

 visible mass is much less than it is on Himalayan 

 stations. From this the general inference is drawn 

 that it is chiefly the subjacent masses that affect the 

 compensation of those visible on the surface. 



/Ml this is quite in accordance with the theory, first 

 advanced by Osmond Fisher, that the " roots " of 

 mountain masses are broader and shallower than the 

 mountains themselves. The time is not far distant 

 when it will be possible to draw an approximate sec- 

 t'on of these roots. It would be interesting to attempt 

 this, in the first instance, by selecting a mountain, of 

 as great a mass as can be found rising abruptly in 

 a flat country, and carrying out a detailed gravimetric 

 survey of tlie whole area, including the mountain 

 and the flat region, for a considerable distance 

 from it. 



The year under review marks an important epoch 

 in the history of the magnetic operations in India in 

 that the preliminary magnetic survey was completed 

 over the whole country with the exception of some 

 frontier regions. Three iso-magnetic charts are pub- 

 lished in the report, showing lespectivelv (i) isogonals, 

 and lines of equal secular change of declination ; 

 (2) isoclinals; (3) lines of equal horizontal force. 

 During the current year the beginning of the detailed 

 magnetic survey was projected. 



Among other points of interest we may note a re- 

 standardisation, with the international metre at Sevres, 

 of Colonel Everest's old lo-foot standard, indicating 

 that no appreciable change has taken place in the 



1 Geneml Report on the Operations of the Survey of Indi.i, .idministcred 

 under the Government of India during 1907-8. Prepared under the direction 

 ..f Colonel F. B. Longe, K.E. Pp. iv + 62, and maps. (Calcutta : Govern- 

 ment Printing Office, igoq.) Price 3.V. 



NO. 2096, VOL. 82] 



lengths of the Indian standard bars during the last 

 forty years. 



Latitude observations were made with the view of 

 eliciting some information as to the cause of the 

 abnormally high deflection of the level found at 

 Chaniana. It was observed that the deflection 

 diminished rapidly in every direction from the apparent 

 centre, arid the conclusion is drawn that its magnitude 

 originates "in a purely local cause, situated either 

 at the surface or at a small distance below it." 



E. H. H. 



NIGERIA AND ITS PLANTS. 

 'T' HE first part of an account of " The Useful Plants 

 ^ of Nigeria," written by Mr. J. H. Holland, now 

 of Kew, but sometime curator at Calabar, appears as 

 one of the Bulletins of Miscellaneous Information 

 (.'Vdditional Series, ix.) recently issued bv the Royal 

 Bot.inic Gardens, Kew. .'\ brief outline of the history 

 of Nigeria is given in the bulletin, followed by a 

 survey of the physical features, climate, peoples, 

 botany, agriculture, and forestry, and finally the first 

 part of the account of the useful plants of Nigeria. 



Mr. Holland complains that " all the maps con- 

 structed so far have been compiled in England from 

 sketches made at various times by numerous sur- 

 veyors independently of each other." This must have 

 been written some years ago, as Government surveyors 

 have been at work since 1902, both in Lagos and 

 southern Nigeria, and some very good maps have 

 been compiled and issued both by the Survey and the 

 Intelligence Department since 1906. In this connection 

 southern Nigeria has to be congratulated on the 

 excellent work done by skilled native surveyors who 

 have been trained on the coast by the heads' of these 

 departments. 



It is only too true that the entrance to most of the 

 rivers is too shallow to admit steamers of any great 

 draught, but it has to be remembered that this diffi- 

 culty has to a certain extent been met by the remark- 

 able build of Messrs. Elder Dempster's steamers, and 

 so far as Lagos is concerned by the indomitable will of 

 Governor Egerton, who already has two great dredgers 

 at work on the Lagos bar. Much larger steamers 

 arc now entering the Lagos lagoon, and the hope 

 is that passengers for Lagos who are now transferred 

 from the ocean-going steamers to branch boats will 

 soon be able to land direct on the marina. When 

 these difficulties are overcome, and the raihvav, already 

 open as far as Jebba and beyond, reaches the hinterland 

 of northern Nigeria, Europe will have easy access to 

 a climate described by Mr. Holland as bracing and 

 delightful, and a country rich in agricultural and 

 mineral wealth. 



Under the heading " Climate," Mr. Holland touches 

 on the remarkable difference between the rainfall on 

 the coast and the interior; " during 1906 the maximum 

 rainfall was 25r4c) ins. at Egwanga, and the mini- 

 mum at Olokemeji 4o'92 ins." The latter place is 

 only ninety miles from the coast. The author also 

 mentions the Harmattan, a wind which coines from 

 the north-east, across the Sahara desert, characterised 

 by excessive dryness. This wind is prevalent during 

 the dry season, and it is this break in the seasons 

 and this Harmattan that we fear are going to 

 decrease the yield of latex of the Para (Hcvea brasilien- 

 sis) introduced from Ceylon. The Director of Agri- 

 culture for the French Colonies on the West Coast of 

 Africa is said to be satisfied, so far as the coast is 

 concerned, that Hcvca brasiliensis is not going to be 

 a success. We know that the trees at Aburi, on the 

 Gold Coast, have ceased to yield latex. From experi- 

 ments, however, in southern Nigeria on trees nearlv 



