PRESIDENT’S ADDRESS. 7 
purpose the work will then cost from twice to three times the present 
amount. One cannot therefore doubt that his Majesty’s Government 
will take advantage of the present offer and opportunity to vote the small 
sum required. This done, we cannot doubt that the German Government 
will complete the chain along the eastern side of Lake Tanganyika, which 
lies entirely within their territory. Indeed, it is no secret that the Berlin 
Academy of Sciences has already prepared the necessary estimates with 
a view to recommending action on the part of its Government. 
Captain Lyons, who is at the head of the survey of Egypt, assures me 
that preliminary operations towards carrying the arc southwards from 
Alexandria have been begun, and we have perfect confidence that in his 
energetic hands the work will be prosecuted with vigour. In any case 
the completion of the African arc will rest largely in his hands. That 
are, if ever my dream is realised, will extend from Cape L’Agulhas to 
Cairo, thence round the eastern shore of the Mediterranean and the 
islands of Greece, and there meet the triangulation of Greece itself, the 
latter being already connected with Struve’s great arc, which terminates 
at the North Cape in lat. 70° N. This will constitute an are of 105° in 
length—the longest are of meridian that is measurable on the earth’s 
surface. 
The Solar Parallax. 
Much progress has been made in the exact measurement of the great 
fundamental unit of astronomy—the solar parallax. 
Early in 1877 I ventured to predict! that we should not arrive at any 
certainty as to the true value of the solar parallax from observations of 
transits of Venus, but that the modern heliometer applied to the measure- 
ment of angular distances between stars and the star-like images of minor 
planets would yield results of far higher precision. 
The results of the observations of the minor planets Iris, Victoria, 
and Sappho at their favourable oppositions in the years 1888 and 1889, 
which were made with the co-operation of the chief heliometer and 
meridian observatories, fully justified this prediction.” The Sun’s distance 
is now almost certainly known within one-thousandth part of its amount. 
The same series of observations also yielded a very reliable determination 
of the mass of the Moon. 
The more recently discovered planet Eros, which in 1900 approached 
the Earth within one-third of the mean distance of the Sun, afforded 
a most unexpected and welcome opportunity for redetermining the solar 
parallax—an opportunity which was largely taken advantage of by the 
principal observatories of the northern hemisphere. Unfortunately the 
high northern declination of the planet prevented its observation at the 
Cape and other southern observatories. So far as the results have been 
‘ «The Determination of the Solar Parallax,’ The Observatory, vol. i. p. 280. 
* Annals of the Cape Observatory, vol. vi., part 6, p. 29. 
