616 HAL 
_ In the year,1678, Halley was electeda Fellow of the 
~~ Royal Society of London ; and, in consequence of the 
dispute between Heyelius and Hooke respecting the use 
of telescopic sights, he went to Dantzic in 1679 for the 
purpose of settling the controversy, by examining the 
method of observation employed by the. Polish astrono- 
mer. He remained at. Dantzic from the 26th of May 
till the 18th July, and returned to England deeply im- 
pressed with a conviction of the wonderful perfection 
of Hevelius’s, instruments, and of the great accuracy of 
his observations. 
In the year 1680, Halley set out for Paris, accompa- 
nied by his friend Mr Nelson, with the view of per- 
forming the grand tour of Europe. In crossing the 
English channel, he obtained a view of the great. comet 
upon its return from the sun; and having been fortu- 
nate enough to observe its descent towards that lu- 
minary, he was able to complete his observations at the 
Royal Observatory. of Paris, which was then under 
the direction of Dominique Cassini, From Paris he 
went toItaly, where he spent the greater part of the 
year 1681 ; but his private affairs obliged him to return 
to England about the end of the year. 
Soon after his arrival in London, Halley married the 
daughter of Mr Tooke, auditor of the Exchequer, and 
took up his residence at Islington, where he put up 
his astronomical apparatus, and pursued with ardour 
his favourite study. With this amiable woman Halley 
lived. 55 years, but was not blessed with any family. 
In the Philosophical Transactions for 1683, he pub- 
lished his Theory of the Variation of the Magnetical 
Compass—a paper of singular merit, in which he endea- 
yours to shew, that the “ whole globe of the earth is 
ene great magnet, having four magnetical poles or 
points of attraction, near each pole of the equator two ; 
and that, in those parts of the world which lie near 
adjacent to any of these magnetic poles, the needle is 
governed thereby, the nearest pole being always pre- 
dominant over the more remote.” 
Our author's. studies were now somewhat interrupted 
by domestic misfortunes. His father had suffered 
greatly from. the fire in London; and having impru- 
dently entered into a second marriage, he was reduced 
comparatively to a state of poverty. His son, however, 
speedily resumed his usual occupations ; and, in the year 
1684, his attention was directed to the subject of Kepler’s 
sesquialterate proportion, from which. he concluded 
that the centripetal force must be inversely as the square 
of the distance. He found himself unable, however, 
to establish this by geometrical-principles ; and having 
applied.in vain for assistance to Dr Hooke and Sir 
Christopher Wren, he at last made. a visit to Cambridge, 
in order to consult Mr Newton, This illustrious mathe- 
matician communicated to Halley. 12 theorems which he 
had written Hpge the. subject, containing his theory of 
ravitation, Halley was sa delighted with the deve- 
opement of this great discovery, that he prevailed. up- 
on Newton to complete his Principia, which was ac- 
tually sabithes in, 1686, under the immediate care of 
Dr Halle , who prefixed to it a discourse of his own, 
and complimented. Newton in an elegant copy of La- 
tin verses. 
In the year 1685 Halley had. been. appointed clerk 
to the Royal Society, and ‘was the principal person em= 
ployed in the publication of its. Transactions. 
n 1686, he published a paper, entitled, An Histori. 
eal Account ¥ the Trade Winds and Monsoons obser= 
vable in the Seas between and near the Tropics, with an 
attempt to assign their physical cause; and in 1687, 
LEY. 
appeared jhis Estimate of the Roantiie of Vapour..raised | 
out-of the Sea by the warmth of the Sun, which gave 
so much satisfaction to the Royal. Society, that they re- 
quested him to pursue the subject..e accordmgly 
published, in 1691, his pene On the. Circulation of the 
Watery Vapours of the Sea, and the Origin of Springs ; 
_in which he first pointed out that fine provision of na- 
ture, by which a constant circulation, of water is kept 
up. between the atmosphere,and the ocean. Hi y 
published in 1687, his paper On the Numbers_and Li- 
mits of the Roots of Cubic and. Biquadratic Equations. 
In 1688, he published a_correct. ephemeris foe that 
year; and in 1691, appeared his paper On the Time 
and Place of Julius Cesar’s Descent upon Great Britain, 
in which he considers it as demonstrated, that Czesar 
landed in the Downs a little to the northward of Do- 
ver cliffs, on the 26th of August, 55 before Christ. In 
consequence of haying had the good fortune to observe — 
the transit of Mercury when he was at St Helena, Hal- 
ley. directed his attention particularly to this class of 
phenomena ; and in 1691, he published. a paper On. ihe 
visible Conjunctions of the Inferior Planets with the Sun, 
in which he has calculated all the transits of Mercury 
from A. D. 1605 te 1799, and all those of Venus from 
918 to 2004. He was fully aware at this time of | 
the great advantages which astronomy would derive 
from the observation of these. phenomena ; and he re« 
marks, that “ the principal use of these conjunctions is 
accurately to determine the distance of the sun from 
the earth, or his parallax, which astronomers have, by _ 
several methads, attempted in vain, while the an 
ness of the angles sought do easily elude the nicest, 
instruments ; but in observing the ingress of Venus ins. 
to, and egress from, the sun, the space.of time between. 
the moments of the internal contacts may, be obtained. 
to a second of time, that is, to ;3. of a second, or,4” of the. 
observed arch, by means of an ordinary telescope and, 
clock that. goes accurately for 6 or 8 hours.” Haley 
had, however, been anticipated in this ingeni 
by: our countryman James Gregory. 
James Gregory. , ie iar ail 
In consequence of Dr Bernard’s resignation, a va. 
cancy took place in the Savilian professorship of Astro-. 
nomy at Oxford. Dr Halley was naturally considered. 
as well qualified for the chair, and, became one of the 
candidates.. Dr David Gregory, however, was the suc- 
cessful competitor ; and ey is known‘ to have lost. 
the office solely from his adherence to.the principles of 
infidelity.. Mr Whiston inform us,“ that Bishop Stil. 
lingfleet. was desired to. recommend him at court; but. 
hearing that he was a sceptic and a banterer of religion, 
the Bishop scrupled to be concerned, till his in,. 
Bentley, should talk with him. about it, which he did, 
But Halley was so, sincere in his infidelity, that he. 
would not so mage #. am Seapeeene ioe pp 
religion, though he thereby was ly to lose a profes« 
pes bi which he did accordingly, and it was then given. 
to Dr Gregory.” saat 
In 1692, Mr Halley resi his. situation as _assist«. 
ant-secretary to the Royal jociety ; and in 1696, when, 
five different mints were established for the recoinage. 
of the silver specie, he was made comptroller of the of- 
fice at Chester. in 1692, Mr Halley published a sin- 
gular paper On the Cause of the Change of the Vari~ 
ation of the Magnelic Needle ; with an Hypothesis of the 
Structure of the Internal Parts of the. Earth. _ In order 
to account for the change in the variation of the needle, 
he supposes that there is an interior globe within the 
earth, separated from the external sphere by a fluid me- 
POS FERRE 
ee our life of. 
