NATURE 



[January 9, 1896 



Pendulum Observations in the Northern and Southern 

 Hemispheres. 



The figure of the earth has been determined by three in- 

 dependent methods of investigation, (i) By abstract mathe- 

 matical calculation of the form which such a body as the earth, 

 rotating as it does, would assume when plastic. (2) By careful 

 measurements of arcs on meridian lines in different latitudes. 

 (3) By pendulum experiments, which have indicated a gradual 

 increase of the force of gravity from the equator towards the 

 poles. 



These three methods, after necessary corrections have been 

 applied, correspond so nearly in their results that probably we 

 have ascertained the true ellipticity of our earth as nearly as is 

 possible considering the irregularities of its surface. But there 

 is one point in connection with pendulum experiments which, 

 although it cannot have escaped notice, has not been treated of, 

 as far as I am aware, in any work on astronomy or geodesy, viz. 

 that all the pendulum experiments hitherto made in the southern 

 hemisphere indicate that the force of the earth's attraction is less 

 in that hemisphere than in the northern. The great navigator, 

 ■Captain Cook, was the first, I believe, to notice this phenomenon 

 in connection with an excellent pendulum clock which he 

 carried with him. He noticed that this clock always went 

 slower at places in the southern hemisphere than it did in the 

 northern hemisphere ; but he did not pursue the question. 



In November 1893, Dr. John Murray read a paper on Ant- 

 arctic research before the Royal Geographical Society, and in 

 the appendix to that paper is a communication from Dr. 

 Neumayer, of the Hamburgh Naval Observatory, giving a table 

 of the results of pendulum experiments hitherto made in the 

 southern hemisphere. In the annexed table I have made use of 

 Dr. Neumayer's collected information, reducing his values of 

 the length of pendulum beating seconds, given in metres, to the 

 corresponding values of the accelerating force of gravity in foot 

 seconds, and I have added, from other sources available to me 

 here, the corresponding values of g at places in nearly similar 

 north latitudes. By comparison it will be seen that the force 

 of gravity in the northern hemisphere exceeds that in the 

 southern hemisphere, in latitudes between 38° and 62°, by a 

 mean of about •010. In Dr. Neumayer's table, experiments in 

 the southern hemisphere are recorded as far as lat. 33° 2' 5" S. 

 (Valparaiso), but I have not been able to obtain here any records 

 in similar latitudes in the northern hemisphere. In the northern 

 hemisphere experiments have been made at Hammerfest 

 70° 40' north latitude, and at Spitzbergen 79° 49' 54" north 

 latitude ; but no corresponding experiments have yet been made 

 in Antarctic regions. 



Taking, however, the values of g at Edinburgh and at Cape 

 Horn, in very nearly the same latitudes, 55° north and south, 

 viz. 32-204 and 32'i94, and assuming that these values will not 

 vary greatly in their difference at the poles ; by a simple cal- 

 culation we find that the centre of gravity of the earth is 

 approximately /^ths of a mile north of the plane of the equator. 

 It would appear from this that in astronomical observations de- 

 pending on zenith distances, and consequently on the direction 

 of the plumb-line, not only must corrections be made for the 

 ellipticity of the earth, but also for the true position of the centre 

 of gravity of the earth, which at the equator must deflect the 

 plumb-line about 15" from the true vertical. 



It is a deeply interesting question whether astronomical 

 observations can be, or have been, made to verify the results 

 obtained by the pendulum. 



Geographically it is a subject which may approximately be 

 investigated by comparing the masses of dry land now standing 

 above the sea-level in the northern and southern hemispheres ; 

 the excess of dry land in the northern hemisphere, at present, 

 being the probable cause of shift of the centre of gravity of the 

 earth northwards. 



In mathematical astronomy it presents an extremely difficult 

 but highly important problem, viz. what effect this position of 

 the centre of gravity of the earth has upon the gyratory motion, 

 producing the precession of the equinoxes, which is caused by the 

 . attractions of the sun and moon on the equatorial protuberance. 



If, as seems probable, a shift in the position of the centre of 

 gravity of the earth north or south of the plane of the equator 

 must produce a shift also in the direction of the axis of gyration, 

 many perplexing geological problems as to varying climates in 

 the same part of the world during different epochs in the world's 

 past history would be at least partially elucidated. There is 

 ample evidence of very widely-extended earth movements oT 



NO. 1367. VOL. 53] 



elevation and depression in the past ; these must have varied the 

 balance of the earth, and if a change in the balance produces 

 also a change in the direction of the axis of gyration, a change 

 in climate follows as a matter of course. 



It is a problem requiring mathematical genius and skill of the 

 highest order for its solution ; but it can be hardly denied that 

 it is of very great scientific interest that it should be correctly 

 solved. 



Finally, I would wish to draw attention to the importance of 

 accurate pendulum experiments being made in the highest 

 southern latitudes attainable by the Antarctic research parties 

 which are either now being organised, or will, it is hoped, even- 

 tually be despatched by the British Government. 



N.B. — The difference in the values of ^between Washington and Mel- 

 bourne, if corrected for difference in latitude, would become -on. Similarly 

 that between Paris and Kerguelen Island would become -010. The variation 

 in the difference at 54°. ^\ 

 local attraction or some inaccuracy in observation. 



Lith and north latitudes may be due to some 



Wellington, New Zealand, 

 November 12, 1895. 



H. S. SCHAW. 



The Metric System. 



It may not be within the recollection of your readers, and very 

 unlikely to be so in that of the British public, that so far back 

 as 1870-71 the Government of India, in the Governor-General's 

 Council, pa.ssed an Act to introduce the metric system into the 

 British dominions in India. However, as all Acts passed by 

 that Government and its Council require the prior sanction of 

 the Secretary of State for India in Council, the measure failed 

 to take its place on the Statute Book of the Empire. His 

 Grace the Duke of Argyle was at that time at the India Office, 

 and it is a matter for much regret that he did not see fit to 

 approve of the measure. That the Government of India did 

 not expect that the Act would be vetoed, is proved by the fact ot 

 its having adopted the system in the State Railway Branch of 

 the Public Works Department, then but recently formed. Sir 

 Guildford Molesworth, K.C.I.E., then Consulting Engineer to 

 the Government of India for Railways, published a series of 

 type drawings dimensioned in the metric system. The Govern- 

 ment further adopted the metre as the gauge of the narrow- 

 gauge .system then introduced for the first time by them. All 

 the platform and other weighing machines sent out were so 

 arranged as to weigh in kilogrammes, tons, and maunds. Had 

 the wise policy of the late Lord Mayo been then approved of, 

 the l"]nglish commercial and .scientific public would not now be 

 clamouring for its adoption in the mother-country, as its great 

 advantages would be patent to all. 



In Ceylon the decimal system has been applied to the rupee, 

 and I have not heard any complaints of inconvenience having 

 arisen from such adoption. 



Cannot a further agitation be started, to move the Govern- 

 ment of England to take steps in the coming session to make a 

 start, at least, in the matter ? It might be notified that, for all 

 Government contracts, no other system would be entertained 

 after January I, 1898. This in itself would give a huge impetus 

 to the movement. V G. Brook-Fox. 



Wfest Ken.sington, W., December 26, 1895. 



