13^7 ) . 
error isgreateft it exceeds not two minuteSj but for the nioft 
pari: it is fo fmalJ, that it may be juftly enough imputed to 
the uncertainty of obferyations. After this he treats more 
particukrJy of the Edipfes of both Sun and Moon, iind the 
manner of Calculacing them 5 he gives an account of the 
Moons motion round its Axis^ and (hows how all thofe va- 
rif)us riurations and iibrations at the Moon, that has hitherto 
fo much puzzled the Philofophers, da only ar^fe from its 
Menftrdoiis uniform rotations , round its Axis 5 from thence 
he paffes to. the ways of determining the magnitudes, denfi- 
-ties; and quantities of matter in the Secundary Planets, and 
the chaoge of Figure both in the Primaries and thera^ that 
muft neceffarily arife if they are fluid from their mutual gra^ 
vitation towards one another, from which he explains the 
Tydes and Modon of the Seas. He ends the Book with a de- 
fcriprion of the Ring of Saturn^ and accounts for all its vari- 
ous appearances feen out of the Earth. 
In the 5th Book the Author treats of Comets, where after 
naving gii'^en the feveral opinions of Philofophers about their 
Place, Duration, Origine, Orbits and Tayls 3 he tells us, that 
certainly they are Bodies that move round the Sun, and differ 
frorn the other Planets in that their Orbits are very oblong 
Elhpfe, wliereas the Planets def cribe Eilipfes which come 
very. near tcCircles, and from this Hypothefis it is eafy to give 
account or the niofc of their Vhsnomena. 3 particularly he 
ihows, that whena Comer comes down from \i% A^hdion^ or 
when it afceods to it^itsTrajeftory will feem to be a right Line^ 
■and may,.be .aflliined as foch.when its motions are to bedeter- 
oiine^wuhmir great niceheft ^ amd upon this account, it is that 
Jvep/^r . a.^ ' fe i^ral d'fhers of the Aftror - Jly iup- 
poie, that they " ftill in f--' jut ever 
reciirr- '-^', T^v; ' ^^Hc^^- ^ ^-^, being 
lieni. ijfly'from the; 'hen 
t;:]o V "lod are car ,:ds by. ithe Air 
.in .wliiC:^ :wac;te'be takes d3ac if this mat- 
ter of iL: . : il^which-frlpre^d at a great diftance from che 
Coniec iuVlO nould lourh^" ind mix with our Atmoiphere^may 
infeci 
