312 REPORT—1905. 
persuasive insistence, through his unwearying diligence in saving Newton all 
cares and trouble and even pecuniary expense, and through his absolutely self- 
sacrificing devotion to what he made an unwavering duty at that epoch in his 
life. Again, he appears to have been the first organiser of a scientific expedition, 
as distinct from a journey of discovery, towards the Southern Seas: he sailed 
as far as the fifty-second degree of southern latitude, devised the principle of the 
sextant in the course of his voyaging, and, as a result of the voyage, ‘he pro- 
duced a General Chart of the Atlantic Ocean, with special reference to the 
deviation of the compass. Original, touched with genius, cheery of soul, 
strenuous in thought and generous by nature, he spent his life in a continuously 
productive devotion to astronomical science, from boyhood to a span of years 
far beyond that which satisfied the Psalmist’s broodings. I have selected a 
characteristic incident in his scientific activity, one of the most brilliant (though 
it cannot be claimed as the most important) of his astronomical achievements ; 
it strikes me as one of the most chivalrously bold acts of convinced science 
within my knowledge. It is only the story of a comet. ; 
I have just explained, very briefly, Halley’s share in the production of 
Newton's ‘Principia’; his close concern with it made him the Mahomet of the 
new dispensation of the astronomical universe, and he was prepared to view all 
its phenomena in the light of that dispensation. A comet had appeared in 
1682—it was still the age when scientific men could think that, by a collision 
between the earth and a comet, ‘this most beautiful order of things would 
be entirely destroyed and reduced to its ancient chaos’; but this fear was taken 
as a ‘ by-the-bye,’ which happily interfered with neither observations nor caleu- 
lations. Observations bad duly been made. The data were used to obtain the 
elements of the orbit, employing Newton's theory as a working hypothesis ; and 
he expresses an incidental regret as to the intrinsie errors of assumed numerical 
elements and of recorded observations. It then occurred to Halley to calculate 
similarly the elements of the comet which Kepler and others had seen in 1607, 
and of which records had been made; the Newtonian theory gave elements in 
close accord with those belonging to the comet calculated from the latest observa- 
tions, though a new regret is expressed that the 1607 observations had not been 
made with more accuracy. On these results he committed himself (being then 
a man of forty-nine years of age) to a prophecy (which could not be checked 
for fifty-three years to come) that the comet would return about the end of 
the year 1758 or the beginning of the next succeeding year; he was willing 
to leave his conclusion ‘to be discussed by the care of posterity, after the truth 
is found out by the event.’ But not completely content with this stage of his 
work, he obtained with difficulty a book by Apian, giving an account of a comet 
seen in 1531 and recording a number of observations. Halley, constant to his 
faith in the Newtonian hypothesis, used that hypothesis to calculate the elements 
of the orbit of the Apian comet ; once more regretting the uncertainty of the 
data and discounting a very grievous error committed by Apian himself, Halley 
concluded that the Apian comet of 1531, and the Kepler comet of 1607, and the 
observed comet of 1682 were one and the same. He confirmed his prediction 
as to the date of its return, and he concludes his argument with a blend of 
confidence and patriotism :— 
‘ Wherefore if according to what we have already said it should return 
again about the year 1758, candid posterity will not refuse to acknowledge 
that this was first discovered by an Englishman.’ 
Such was Halley's prediction published in the year 1705. The comet pursued its 
course, and it was next seen on Christmas Day 1758. Candid posterity, so far 
from refusing to acknowledge that the discovery was made by an Englishman, 
has linked Halley’s name with the comet, possibly for all time. 
We all now could make announcements on the subject of Halley’s comet ; 
their fulfilment could be awaited serenely. No vision or inspiration is needed— 
calculations and corrections will suffice. The comet was seen in 18385, and 
it is expected again in 1910. No doubt our astronomers will be ready for it: 
