vi Transactions of the South African Philosophical Society. 



which were sharply depicted on the plate. He had long been 

 considering the best means of completing Argelander's Survey of 

 the Heavens, and photography seemed to be the means of doing it. 

 Accordingly, with the aid of a grant from the Government Grant 

 Fund of the Eoyal Society, the services of Mr. Woods were secured, 

 and the work was begun in 1884. When in 1887 the International 

 Scheme for the "Carte du Ciel " was arranged, the Eoyal Society 

 seemed to think that Dr. Gill's less ambitious plan need not be 

 completed. He (Dr. Gill) did not take this view, especially as Prof. 

 Kapteyn, of Groningen, had already undertaken the more laborious 

 part of the work, viz., the measurement of the plates and their 

 reduction, and he resolved to carry out the work. The international 

 programme was naturally a much more ambitious one, but it would 

 be at least fifty years before it could be carried to completion, and 

 meanwhile some such complete nomenclature of all stars likely to be 

 used for the ordinary purposes of the astronomer was a pressing 

 necessity for the astronomer in the southern heavens. The work 

 having been completed, the Lords Commissioners of the Admiralty 

 undertook its publication, and the first volume was now before the 

 Society. The other two would soon follow. 



Vols. VI. and VII. represent work of an entirely different kind. 

 They contain the observations made on the minor planet Iris in 

 1889, on the minor planets Victoria and Sappho in 1890, with the 

 heliometers at the Cape, Yale, Liepzig, Gottingen, and Bamberg, 

 and of meridian observations of these planets and comparison stars 

 made at twenty-two different observatories. The whole of this work 

 was based on plans which Dr. Gill had proposed for determining the 

 great fundamental constants of astronomy, viz., the Solar Parallax 

 and the Mass of the Moon. The meridian observations had been 

 discussed by Dr. Auwers, of Berlin, the heliometer observations of 

 Iris by Dr. Elkin, and those of Victoria and Sappho by Dr. Gill. 

 The whole of this labour had resulted in the following figures : — 



Parallax of the sun 8 ,/y 802 + O005 probable error. 



Mass of the moon in terms of the earth, y- r 4iy^- 



And these values have been adopted for international use at the 

 Paris Conference of Astronomers in 1896. 



The value of the solar parallax was the fundamental constant of 

 astronomy, and apparently in the judgment of his colleagues these 

 observations and this discussion had solved a problem which all the 

 numerous Transit of Venus expeditions of 1761, 1769, 1874, and 

 1882 had failed to solve, viz., to determine the mean distance of the 

 sun within t <jVo P ar ^ °f ^ s amount. 



