Royal Society. 7 
fhe viable Con]un5lions of the inferior Planets ivitb the Sun ^ by 
Mr. Halley, Phil. Tranf. N° 1^3, p. 511. Tranjlatedfrm 
the Latin. 
THAT Mercury and F<?;7«5 do enter the diflc of the fun and 
appear thereon like fo many black Ipots, is evident, both 
from the principles of Ibund aftronomy, and undoubted oblerva- 
tionsj but by what laws, or conditions, or in what period of 
years thefe phienomena of^r themfelves to our view, has not been 
determined by any of our modern aftronomers ; on which account 
Mr. Halley thought it would not be unacceptable, if he ferioufly 
applied himfelf to this difquifition, and cleared up a fubjedt fo 
perplexed and fo little underftood. 
It is felf-evident that thefo phafes of thefe planets always hap- 
pen in their conjun<^ions with the fun, when rerroorade- viz, 
when the fun is^ fo near their nodes, that the latitude of the 
planet, in its conjunction with the fun, does not exceed the femi- 
diameter of the latter 5 that the limits and conditions of theie 
conjunctions may be the more eafily inveiligated, and fince the 
elements of the calculation are entirely different, each planet is to 
be treated of apart: And therefore to begin with Mercury^ it is 
certain that according to late and accurate obfervations, the af- 
cending node of this planet, in this century, viz. March i6'9r, 
is found near the 15° of 'Taurus , or rather ato S. 15^ 44' from 
the firft ftar of Aries 5 and the oppofite defcending at (j S. 1 5"* 
44' from the fame ftar 5 the inclination of the plane of Mercury^ 
orbit to the ecliptic according to Kepler is 5° 54' which is nearly 
exaCt : Now it appears from the moft approved hypothefes, that 
the diftance of Mercury from the fun, when in the alcendin<y 
node, is 31355 parts, of which the mean diftance of the fuS 
from the earrth is 1 00000 5 but when it is in the other node, tha^ 
diftance, meafured in the fame parts, is 45908 : The fun, *wheQ 
oppofite to the afcending node, is diftant from the earth, in con« 
junaion therewith, 5^8955 parts, but in the other node, the fame 
diftance becomes 101007 5 and therefore Mercury, in conjunaion 
with the fun at the afcending node, is diftant from the earth 
<)7 591 parts, bux at the defcending node 55(^995 which widely 
differing from each other, thefe conjunaions, that happen in 
different nodes, are alfo to be confidered feparately. 
Let Mercury, when retrograde, be in a central conjiinaion 
with the fun in the afcending node, in the month of 06iokrt 
and from the above hypothefes we ihall have as follows 5 
The 
