554 



NA TURE 



[September 27, 1906 



have made it possible to tatce the three negatives necessary 

 for their method of colour photography in three seconds, in- 

 cluding the time required for changing the plates and 

 light filters, when the light is only moderate and the lens 

 aperture //i6. In the central court, besides a great deal 

 of apparatus and several demonstrations of processes, the 

 Adhesive Dry Mounting Co. shows its method of mount- 

 ing by warm pressure. The Ozotype Co. shows in the 

 north room several examples of " ozobrome " prints. These 

 are quite a new departure, a carbon print being produced 

 by means of a bromide print without exposure to light, 

 the silver image in the bromide print reducing the 

 bichromate in the carbon tissue by mere contact. The 

 original bromide prints and the carbon copies are shown 

 side by side. C. J. 



GEODETIC OPERATIONS IN SOUTH AFRICA.' 

 T T will be admitted that the Administration of Southern 

 Rhodesia acted wisely in accepting the timely counsel 

 which Sir David Gill brought under its consideration. 

 Some ten years ago His Majesty's Astronomer at the Cape 

 pointed out to Lord Grey, who then administered the 

 government of the colony, the desirability of basing the 

 land tenure on a properly established system of survey. 

 The adoption of such a course would not only afford the 

 means of supplying a sound and incontrovertible evidence 

 of title to the possessor, but would protect the Government 

 against the perpetration of fraud and tend to diminish 

 future litigation. Sir David Gill does not hesitate to say 

 that in Cape Colony large tracts of land have been stolen 

 •from the Government, either through the wilful shifting of 

 beacon marks or from carelessness due to inadequate 

 surveying. Sir David Gill did not lay any great stress 

 upon the scientific value that necessarily attaches to accurate 

 measurement conducted on a large scale ; but this point 

 was not neglected, and the work was planned so as to 

 give the greatest assistance to economic requirements, and 

 at the same time to forward scientific interests. The one 

 purpose was effected by carrying a chain of triangles east- 

 wards from Bulawayo, covering the most thickly populated 

 and important parts of the country, the other by extending 

 the chain north and south along the thirtieth meridian, so 

 that it might form part of the great arc of meridian which 

 it is proposed to extend from the south of Natal to the 

 Mediterranean. The actual district surveyed e.xtends from 

 about 16° to 20° south latitude and from 28° to 31° east 

 longitude. 



Sir David Gill sketches the history of the work accom- 

 plished in successive years, from which can be gathered 

 something of the difficulties which Mr. Simms and his 

 assistants encountered and overcame. Abnormally wet 

 seasons, illness among the staff, the necessary burning of the 

 grass and the rising of the smoke preventing the measure- 

 ment of horizontal angles, loss of cattle, and in one instance 

 the destruction of the theodolite, are a few of the troubles 

 that beset those who attempted geodetic operations in an 

 unsettled country ; but, notwithstanding these drawbacks, 

 there remained only three stations south of the Zambezi 

 which were not fully connected with the scheme of triangu- 

 lation proposed. As the work is extended northwards these 

 stations will be occupied, and thus form a useful link in 

 the two systems. 



A matter of great interest in the report from a scientific 

 point of view consists in the critical examination of the 

 Jaderin wires used in the measurement of the base lines. 

 This apparently convenient form of measurement was, it is 

 believed, adopted by the Russian geodesists in the work 

 connected with the Spitsbergen base, but in this country 

 the apparatus has not been submitted to any very thorough 

 test, and figures for the first time on a large scale in the 

 geodetic survey of South Africa. Two wires, one of steel 

 and the other of brass, constitute a " pair," and, as a rule, 

 were used in this form. Each wire is about 1-65 mm. in 

 diameter, and is stretched by an accurate spring balance 

 with a tension of 10 kilograms. The length of three pairs 



1 Report of the r.eodetic Survey of part of Souihern RhoHesIa executed 

 by Mr Alexander Simtn's, Oovernment Survevor, under the direction of Sir 

 David Gill, KCB, F.R.S., His Majesty's Astronomer at the Cape. 

 Pp. xiv+146. (Cape Town, IOCS.) 



NO. 1926, VOL. 74] 



was each So feet, but two others of 160 feet and 320 feet 

 respectively were used in crossing streams and gulleys. 

 Another form of the same apparatus, occasionally used, 

 consisted of a wire of " invar " nickel-steel and a wire of 

 another alloy having a coefficient of expansion about the 

 same as that of brass. The absolute length of each of 

 these pairs was determined by repeated comparisons with 

 a base line 80 feet in length, measured with a standard 

 bar apparatus ; but even the length of this base could not 

 be assumed to be constant. The partially decomposed 

 quartzose slate beneath the piers which carried the fiducial 

 marks appeared to change slightly in position, especially 

 after rain, and the length of this base as measured in the 

 wet and dry seasons differed by half a millimetre. Constant 

 measurement with the bars removed any source of error 

 from this cause, since the change of length between the 

 beginning and end of a set of wire comparisons was 

 practically insensible. 



But the real source of error in the use of the Jaderin 

 wires lies in the fact that the ordinary steel and brass 

 wires are liable to change of length, due to re-arrangement 

 of the molecules of the constituent metals which takes place 

 independent of temperature after these molecules have been 

 violently disturbed. The tendency in all new drawn wires 

 is to shorten, very markedly at first, and to diminish in 

 amount as a more stable arrangement of the molecules is 

 established. In a postscript, however, it is stated that, as 

 the result of experiments conducted at the International 

 Bureau of Weights and Measures, it is found possible by 

 careful annealing and special mechanical treatment to 

 render the arrangement of the constituent molecules of 

 " invar " wires practically stable, and that such wires can 

 be used as standards. Such wires, however, are not 

 examined here. As an evidence of the change of length in 

 the wires actually used, we may quote the following : — 

 The length of a standard pair, at a temperature when both 

 components were of equal length, was found to be in 



April and May, 1S9S 24382-07 mm. 



October and November, 1898 ... 24381-84 ,, 

 Two base lines were measured in the course of the work, 

 one of iif miles and the other of 13J miles. The first, 

 known as the Inseza base, was measured in three sections, 

 the second in seven, each section being measured in oppo- 

 site directions. As an indication of the accuracy attained 

 we give the repeated measures in the shorter base : — 



We have not space to quote the results in the case of 

 the Gwibi or longer base, but the results there are even 

 more accordant, the average discrepancy amounting to only 

 one in a million and a half. W. E. P. 



UNIVERSITY AND EDUCATIONAL 

 INTELLIGENCE. 

 The celebration of the four hundredth anniversary of 

 the foundation of the University of Aberdeen began on 

 Tuesday, and will continue for several days. The com- 

 memoration has been planned on a magnificent scale, and 

 the arrangements have been perfectly organised. The 

 formal proceedings opened on Tuesday morning with a 

 service at King's College in commemoration of the found- 

 ing of the University by Bishop Elphinstone. In the after- 

 noon, at a reception given by the Chancellor (Lord 

 Strathcona) and other high officers of the University, the 

 delegates of the British, colonial, and foreign universities 

 were presented to the Chancellor and delivered their 

 addresses. In the evening a banquet was given by the 

 Lord Provost and the corporation. Among the distin- 

 guished foreigners who are taking part in the celebrations 

 are : — Prof. H. Becquerel. Prof. Behring, Dr. C. De 



