'■58 



NA TURE 



[January 12, 1899 



mounlcd on a horizontal revolving ring or annular frame, pro- 

 vided with rollers at suitable intervals apart, which roll on a 

 fixed circular track or rail firmly secured to ihe wall of the 

 building. The dome is made in two halves, divided in a vertical 

 plane through the centre, and hinged at one extremity of this 

 division at two of their adjacent corners to a pin fixed to the re- 

 volving ring or annular frame above mentioned. At the opposite 

 corners of the two halves of the dome are fixed rollers, one at 

 each corner, and two other rollers are supplied 90' from the first 

 pair, one in each half. These rollers roll on the .surface of the re- 

 volving ring, or on short races, in such a manner as to support 

 the two halves of the dome on the horizontal revolving ring, and 

 permit of their being opened or closed. The opening is, of 

 course, a wedge-shaped one. The two halves of the dome being 

 mounted on the ring, which is capable of revolving by means of 

 the rollers resting on the circular rail, the wedge-shaped opening 

 in the dome can be brought to face any part of the sky." 



It may be mentioned as a further advantage of this arrange- 

 ment that in the winter season, when the dome may be covered 

 with snow, it does not prevent it being opened, as is so fre- 

 quently the case with domes with shutters ; and, furthermore, 

 it gives facility for any design of dome being used, which a 

 shutter renders impossible. 



A New Astronomical Periodic.-vl. — We have received a 

 circular from the Manora Ob.servatory in Lussenpiccolo, inform- 

 ing us that a new illustrated astronomical periodical will be 

 published from that observatory, with Herr Leo Brenner as 

 editor. Ten numbers will be issued during the year, and these 

 altogether will contain 400 pages and over 100 illustrations. 

 The price for the ten numbers is stated to be twelve shillings, 

 post free. 



CONFERENCE OF THE INTERNA TIONAL 

 GEODETIC ASSOCIATION} 

 'T'HE twelfth general conference of the International Geodetic 

 Association was held at Stuttgart on October 3-12, 1898. 

 Fifteen countries of the nineteen composing the Association 

 were represented. Of the thirty-seven delegates present 

 fifteen came from Germany, five from France, three from 

 Italy, two from Switzerland, two from Japan, and one each 

 from Belgium, England, the Netherlands, Austria-Hungary, 

 Russia, Sweden, Spain, Mexico, and the United States. 

 Besides the delegates, eighteen invited guests appeared, making 

 a total of fifty-five persons present at the meetings. By far the 

 greater part of the time was naturally taken up in reading the 

 regular reports by the delegates on the geodetic work accom- 

 plished in their respective countries since the last general 

 conference. 



Of special interest was the contribution by Prof. Helmert 

 on the activity of the Central Bureau of the Association at 

 Potsdam. The following work was described : (l) The system- 

 atic deviations of the plumb line in connection with the 

 European arc on the 52° of north latitude. (2) The inter- 

 national latitude service. (3) .Absolute determinations of gravity. 

 The international latitude service will be inaugurated during 

 the summer of 1899 at four stations under the direct control 

 and at the expense of the Association. Observations at two 

 additional stations will be undertaken, for which the Central 

 Bureau will supply only a part of the funds necessary. -Vlthough 

 the mathematical conditions are not essentially changed by the 

 introduction of Cincinnati and Tschardjui, there is great ad- 

 vantage from the fact that any systematic errors in the regular 

 stations will be more readily discovered. It is a fortunate 

 coincidence that the observatory at Cincinnati happens to be 

 precisely on the parallel of latitude chosen for this work, and it 

 IS, moreover, a matter for congratulation that Russia is ready 

 and willing to aid in the undertaking, to the extent of estab- 

 lishing and superintending the station at Tschardjui. 



The latest results from pendulum obseivations arc with 

 reference to changes of the force of gravity with elevation, and 

 the derivation of a new formula for the length (L) of the seconds 

 pendulum at the sea-level. Erom a discussion of over 500 

 stations the conclusion is reached that what is usually known 

 as continental attraction amounts jir.-ictically to nothing, and 

 that in general the change of the force of gravity at any point 



* Abridged from :\n otficial report by Mr. E. D. Preston to the Supcr- 

 ititcndcnt of the C^>a*,l and Geodetic Survey, published in Science. 



on the earth's surface depends purely and simply on the 

 Newtonian law of the inverse square of the distance. The 

 introduction of a spherical function of the third order in the 

 formula for L, alluded to before, foreshadows the determination 

 of a different curvature for the northern and southern hemi- 

 spheres of the earth ; yet the coefficient appears so small thai 

 the inequality cannot as yet be safely predicted. The com- 

 pression given is 1/297, ^"'' ^^^ equatorial value of the force of 

 gravity is about I 13,000 greater than that now accepted. The 

 investigation of the relation between disturbances in the force 

 of gravity and deviations of the plumb line is one of the most 

 interesting problems of the near future. 



Three matters of universal interest were brought before the 

 Association, and suitable action was taken thereon. These 

 were : (i) " The determination of the figure of the earth by the 

 measurement of arcs and the determination of the force of 

 gravity." (2) " The remeasurement of the Peruvian arc." (31 

 "The redetermination of the difference of longitude between 

 Paris and Greenwich." The first two subjects were introduced 

 as resolutions by the United States delegate, and brought out 

 interesting discussions. The first w^as proposed for the sake of 

 directing the attention of the Association more specifically to 

 the prime object of its existence. No one doubts the utility or 

 necessity of a complete study of the law governing the changes 

 of latitude, but its ultimate bearing is rather one of a.stronomy 

 than geodesy. The funds of the .Association are now being 

 devoted largely to the latitude question, and the time seemed 

 fitting to suggest work more directly in the line of its avowed 

 purpose — the measurement of the earth. The object of the 

 resolution was, therefore, in the nature of a recall to the 

 original conception of its being, and bespoke in the interest of 

 pure geodesy an application of its resources to a realisation of 

 the idea of its founders. 



The remeasurement of the Peruvian arc now appears to be 

 assured. It may be worth while just here to recall the essential 

 features of this work. One hundred and sixty years ago, when 

 it was a disputed question whether the polar or equatorial 

 diameter of the earth was the longer, the Erench .-Vcadeniy 

 decided to make one supreme effort to settle the point. To 

 this end, two arcs were measured : one on the equator (now 

 known as the Peruvian arc, although it is really in Ecuador) ; 

 and the other in Lapland, as near the pole as possible. These 

 two arcs, confessedly inaccurate in the light of modern geodesy,, 

 have been employed continually in the determination of the 

 earth's figure. Situated as they are, near the extremities of the 

 quadrant, their influence is great on the shape deduced, so that 

 one of the pressing needs of the day in the measurement of the 

 earth is a redetermination of their lengths. It is proposed to 

 make a reconnaissance during the summer of 1S99, report the 

 results thereof to the Paris conference of 1900, and then decide 

 definitely on the plans of final measurement. It is universally 

 conceded that France should be given the first chance to act, 

 not alone because the first measure was made by her, but also 

 because the conference of 1889 relinquished in her interest 

 further consideration of the subject. 



The Russians and Swedes, in a quiet sort of way, are 

 measuring an arc between the parallels of latitude 774° andSlJ" 

 in Spitsbergen. The triangulation will require two summers 

 and part of one winter, and will cost 100,000 kronen (5500/.), 

 exclusive of cost of vessels furnished by the governments. The 

 field work will be finished in 1900, and the computations two 

 years later. Fifty stations will be occupied. The sides range 

 in length from ten to one hundred and thirty kilometres, and 

 the bases, of which there will be only two, are to be measured 

 with Jaederin's steel tape line, twenty metres long. 



The difference of longitude between Paris and Greenwich 

 came up again for investigation. Nothing seems to remain 

 but to study the conditions of the work of iSSS and 1892, and 

 reconcile, if possible, the outstanding difference. The mat/er 

 has been referred by the International Geodetic .\ssocialion to 

 the directors of the two observatories, and a definite result will, 

 doubtless, soon be made known. 



The variation of the latitude seems to be at present an ab- 

 sorbing question before the Association ; and there results from 

 action taken at the Stuttgart meeting the following status : — 

 Six stations will be established during the summer of 1S99 on 

 the parallel of latitude 39° 8'. These will be distributed in 

 longitude as follows : one each in Jap"". Turkestan and Italy, 

 and three in the United States. The American ones will be 

 located at Gaithersburg, Md. ; Cincinnati, O. ; and Ukiah, 



NO. 1524, VOL. 59] 



