i 
NS ee RE + en NNN 
‘ramour Pink, in which 
tober 1698. Having sailed along the African coast, he 
HALLEY. 
dium; ‘that they revolve about the same diurnal axis 
™ nearly in 24 hours, the outer ing: either a 
 Jittle slower or faster than the internal the 
a etic poles both of the external in- 
: ed globe, are distant from the poles: ; 
and that the variation arises from the in the re- 
 Jative distances of the external and internal poles, in 
of the difference of their daily revolutions. 
“consequence 
The whole of this paper, though marked by then 
 nuity of Henthor ie chaxscteried by an Pana 
‘of speculation, in which he was not accustomed to in- 
dulge. He even goes so far as to say, that there may be 
‘several internal spheres separated by atmospheres, the 
concave side,of each shell being made up of magnetical 
matter ; and he considers it as by no means improbable, 
that these different spheres may be occupied by living 
The concave arches,” says he, “‘ may, in se- 
bei 
oon aig shine with such a substance as invests the 
surface of the sun ; nor can we, without a boldness un- 
becoming a philosopher, adventure to assert the im- 
ibility of peculiar luminaries below, of which we 
we no sort of idea”. > 
- Till the year 1698, Dr Halley continued to enrich 
the Philosophical Transactions with various memoirs 
‘on the price of annuities on lives ; on the foci of lenses ; 
on the roots of equations, and on different subjects = ma= 
thematics, meteorology, antiquities, astronomy, and op- 
tics. He now, however, conceived the design of making 
an extensive voyage to determine the variation of the 
needle in different parts of the world. For thi8 pur- 
‘pose, King William appointed him in of the Pa- 
e set sail on the 20th of Oc- 
crossed to the coast of America, going some degrees 
‘south of the line. . His crew having begun to lose their 
health, and_his officers to become mutinous, he pro- 
ceeded to the West Indies to get them exchanged ; and 
_ when he found this impracticable, he returned to Eng- 
land, where he arrived early in July 1699.. When hs 
lieutenant had been tried and cashiered, he ‘again set 
sail on the 16th of September 1699, and after having 
made observations at St Helena, the Brazils, Cape 
Verd, Barbadoes, Madeira, Canaries, the coast of Bar- 
bary, he proceeded in a southerly direction till he was 
stopped by the ice in the south latitude of 53°. Ha- 
ving thus accomplished the object of his voyage, he re- 
turned to Britain, and anchored in Long Reach on the 
7th of September 1700. From this voyage he received 
the title of Captain in the Navy, and through the in- 
fluence of Queen Caroline, he enjoyed half pay duri 
the remainder of his life. The results which Dr Hal- 
Jey obtained during this voyage were published in 
1701 in his general chart, which exhibits the variation 
of ‘the needle in all the seas frequented by navigators.* 
In 1701, Mr Halley was sent by the King to observe 
‘the course of the tides in every part of the English 
Channel, and to ascertain the geographical positions of 
the principal headlands. This task was accomplished 
in 1702, and the results were published in a large . 
chart of the English Channel. 
The Emperor of Germany having resolved to form 
a commodious harbour in the Adriatic, Halley was sent 
by Queen Anne to inspect the two ports on the coast of 
almatia. He set out on the 22d of November 1702, 
and went to Istria by the wy. of Holland and Germa- 
; but, in consequence of the opposition which the 
‘Dutch made to the scheme, it was laid aside. The 
611 
Emperor, however, when he saw him at Vienna, made Halley. 
him a present of a rich diamond ring from his own fine "VY 
ger, and gave him a letter of recommendation written 
in his own hand to Queen Anne. No sooner had he 
returned to England, than he was a second time dis. 
patched to Germany on the sume errand. In passing 
through Hanover, he supped with the Electoral Prince, 
afterwards oe George I. and his sister the Queen of 
Prussia ; and after having been presented to the Empe- 
ror on the evening of the day on which he avived ot 
Vienna, he set out with the chief engineer for Istria, 
when the fortifications of Trieste were, by his advice, 
ired and enlarged. 
pon his return to England in November 1703, he 
succeeded to the Savilian professorship of geometry at 
Oxford, which was vacant by the death of Dr Wallis; 
and the university at the same time conferred upon him 
the honorary title of doctor of laws. As soon as he set- 
tled in this new situation, he , in conjunction 
with his colleague Dr Gregory, to publish the works of 
the ancient geometers, in pursuance of the plan recom- 
mended by Sir Henry Saville. He translated from the 
Arabic into Latin, Apollonius de Seclione Rationis : 
(See Anatysis, vol. i. p. 722.) and he restored the two 
books of the sume author, De Sectione Spatii, from the 
account given by Pappus. This work appeared in 
1706. Dr Halley assisted also in p ing for the 
press, the Conics of Apollonius ; and he supplied the 
whole of the 8th book which had been lest. ‘This work 
appeared in 1710; and contained also Serenus On the 
ection of the Cylinder and Cone, which was printed from 
the original Greek, with a Latin translation. In 1708, 
Dr Halley published the Miscellanea Curiosa, in 3 vols. 
8vo, which contained several original articles by himself. 
On the death of Sir Hans Sloane in 1713, Dr Hal- 
ley was appointed secretary to the Royal Society. In 
1716, he published his paper On the art of living under 
water, which contains an account of his diving bell, and 
of the experiments which he made with it at great 
depths in the sea: (See Divine Betz, vol. viii. p. 11, 
be At the death of Mr ener * thowgh —- 
was appointed astronomer royal ; an e 
ees seddliad the 64th year of his age, he entered upon 
the duties of his new office with a degree of juvenile ar- 
dour ; and without the help of an assistant, he continued 
for 20 years to make celestial observations with the most 
surprising and unremitting assiduity. In the space of 
9 years, a period of the moon’s apogee, he made no fewer 
than 1500 observations on the moon’s right ascension, 
the object of which was to determine the i 
ties of her motion, and to furnish navigators with the 
most correct means of finding the longitude at sea. He 
gave an account of this plan in the Phil. Trans. for 
1751, inhis Proposal for finding the Longitude at Sea 
within a e, or 20 Leagues. Inan appendix to 
the second edition of Street’s Caroline Tables, Halley 
had suggested this method of oe the longitude so 
early as 1683 and 1684 ; and he now shews, from a com- 
son ofthe lunar tables with accurate observations, 
the longitude may always be determined to with- 
in 20 leagues under the equator, and 15 leagues in 
the British Channel. , 
Dr Halley was constantly employed in perfecting 
his tables of the planets. They were drawn up in 
1725; but he was unwilling to publish them till they 
were made as ect ‘as he could. In 1729, he was 
elected a foreign member of the Academy of Sci- 
’ * The original journals of Dr Halley’s two voyages, were published by — Alex, Dalrymple, Big. in 1775, in » thin quarto volume, 
