£ 426 3 
XXIV. Advertifement of the expected Return of the Comet of 
153 2 and 1661 in the Tear 1788. By the Rev . Nevil 
Mafkelyne, D* D* F. R. S. and AJlronomer Royal . 
Read June 29, 1786. 
T HE comet of 1531, 1607, and 1682, having returned 
in the year 1759, according to Dr. Halley’s pre- 
diction in his Synopfs Afronomiee Cometicce , firft publifhed in 
the Philofophical Tranfa&ions in 1705, and re-publiflied with 
his Aftronomical Tables in 1749, there is no reafon to doubt 
that all the other comets will return after their proper periods, 
according to the remark of the fame author. 
In the firft edition of the Synopfs he fuppofed the comets of 
1532 and 1661, from the fimilarity of the elements of their 
orbits, to be one and the fame ; but in the fecond edition he has 
feemed to leflen the weight of his firft conje&ure by not 
repeating it. Probably he thought it beft to eftablifh this new 
point in aftronomy, the doCtrine of the revolution of comets 
in elliptic orbits, as all philofophical matters in the beginning 
fhould be, on the moft certain grounds ; and feared that the 
vague obfervations of the comet, made by Apian in 1532, 
might rather detract from, than add to, the evidence arifing 
from more certain data . Aftronomers, however, have gene- 
rally acquiefced in his firft conjecture of the comets of 1532 
and 1661 being one and the fame, and to expeCt its return to 
its perihelium accordingly in 1789. * 
The 
