i88o.] 
Edmund Halley . 
93 
with which he beheld the gradual rising of the Centaur, 
Argo, Crux, and the Nubeculae of Magellan, whose pale 
phosphorescent radiance contrasts with the dark spot through 
which the terrestrial spectator catches a glimpse of the ultra- 
planetary depths of space. 
Arrived in St. Helena, then overgrown with forests and 
rare shrubs, now extinCt for ever, he appears to have landed 
at James’s Fort, in Chapel Valley, late in the year, and 
must have found no small difficulty in the selection of a site 
for his temporary observatory ; but doubtless tempted by the 
unusual clearness of the season, he selected a magnificent 
situation on the northern side of the central mountain, to 
which he must have had considerable difficulty in transporting 
his instruments, as even with the present modern roads 
wheeled transport is most limited and precarious. Under 
Governor Field, however, with slave labour and royal 
auspices, Halley industriously set to work towards the com- 
pletion of the catalogue of the southern stars, and delineated 
a planisphere of their projection. It was here, says Prof. 
Forbes, that “ Halley was the first to see clearly what a pow- 
erful means of determining the sun’s parallax an observation 
of contaCt really is. So far as I can discover, he first men- 
tions the method in a letter to Sir Jonas Moore, written at 
St. Helena in 1677,* just after having seen a transit of 
Mercury. The exactness with which he believed the time 
of contaCt to be determinable led him frequently afterwards 
to urge his countrymen to make every effort to utilise the 
method on the occasion of the transits of 1761 and 1769* 
when he should be dead.t And thus, in addition to his 
celebrated prediftion of a comet, he left a second legacy to 
his successors, who, as Englishmen, might be entitled to be 
proud of his foresight, though he could not live to reap the 
glory of it.” — (“ The Coming Transit of Venus,” by Prof. 
George Forbes, “ Nature,” April 23, 1874. 
“ Halley saw (what many people fail to see even now) that 
the great accuracy of the method consists in this, that in one 
second of time Venus moves over about 0*02" ; and if we can 
determine the time of contaCt, with an error of no more than a 
second, we are measuring the sun’s parallax with an error of 
no more than 0*02 of a second of arc. Halley even pointed 
out the best stations for observations.” — {Ibid.) 
Ninety-four years subsequently to this letter Dr. Maskelyne 
* Hooke’s Ledtures and Collections. 1678. 
f Catalogus Stellarum Australium ; also Phil. Trans., 1694 and 1715. 
