Ix President'' s Address. [^^g- 28 y^- 



hemisphere by Dr. Elkin. The Heliometer was also used last October' 

 and November for a determination of the sun's distance by obser- 

 vations of the minor planet Iris by Dr. Gill and myself, and again 

 during the last three months of the minor planet Victoria by Drs,- 

 Auwers and Gill, who have secured over 3,000 observations. The 

 degree of accuracy that can be secured with this instrument is truly 

 astonishing, and if we are fortunate enough to secure a sufficient 

 number of corresponding observations in the Northern hemisphere 

 I am confident that the vexed question of the Sun's distance will be' 

 settled within very small limits from these observations. 



As an instance of what this instrument is capable of, I will quote 

 some results given by Dr. Gill in a paper read before the Royal Astro-^ 

 nomical Society in 1888. He gives some measures in that paper of 

 /3 Centauri from a couple of faint stars at nearly equal distances 

 on opposite sides of it, and all he is concerned with for the determ- 

 ination of the parallax is the difference of these distances ; but takings 

 the sum of these distances amounting to about 10,000 seconds of- 

 arc the probable error of this very considerable distance from a single- 

 observation is only 0'"2 of a second of arc, 



GEODETIC SURVEY.. 



The Geodetic Survey of South Africa has been gradually progressing: 

 under the able management of Major Morris, RE. I mentioned in 

 my address last year that an unexpected discrepancy had been found 

 between the Geodetic and Astronomical latitudes in the neighbourhood ' 

 of Port Elizabeth. This has been most carefully investigated by 

 Major Morris since then and he finds that the discrepancy extends^ 

 to several places in the neighbourhood. Port Elizabeth and Coega' 

 Kop shew discrepancies of nearly the same amount and sign, while 

 Zuurberg and Berlin shew as much discordance in the opposite 

 direction. It would seem that somewhere within the area included' 

 by these points the density of the underlying strata is considerably 

 greater than the average density of the earth : the station at Driver's 

 Hill seems to be very near the line of no discordance. Similar 

 anomalies have been found in many parts of the world, but still it 

 is to be hoped that this one will be investigated more fully. A 

 determination of the longitudes of the most important ports on the 

 West Coast of Africa is being carried out at the present time by 

 Commander Pullen, R.N., and myself. Observatious for time are 



