f8o 7 ) 
had an extraordinary Trayn ? fometimes 45, 60 > 75, yea ro4degr, 
long 3 as alfo that for forne time it (hone all nighty and now and 
then feem'd to break out into Lightning. To all which he 
adds the Obfervations of the Comets feen A.i6^j 0 1612,1661 9 
1664,16655 of which the laft four were diligently obferv'd and 
are exa&ly defcribed by himfe'f. 
As for the Theory, whereby the Author renders an Account or 
all the Phenomena of 'Comets , he fuppofeth,that they all move in 
a Str eight Liw 0 by which fuppofition (firft fuggefted by Kepler) 
and no other, that he can imagine, he efteems that all the A p- 
pearances of them, how infoluble foever elfe they feem, may ve- 
ry eafily be explicated, efpecially fuppofing the Sun in the Cen- 
ter of the Univerfe, and the Annual motion of the Earth^though 
he fuggefts alfo a way of faving the (aid Rectilinear motion even 
without deftroying the fyfteme of Ptolomj. But yet he would 
not be understood fo ftri&ly in aflerting that fireight motion,but 
that Comets may more orlefs deviate from that ftrcightnefs , 
both in appearance, and really 3 the former ariling from the va- 
rious fight of them, and their various diftance from the Earth 
and the Sun, and the Annual motion of the Earth-, the Utter , 
from the matter of their Bodies and Nucleus's ( as he calls the 
fubftance of their Bead) not increafingnor decreasing uniformly 
on all fides. To which he adds the consideration of a motion 
imprefs'd, and that of an Inclination of tk^^^i^^hk tqp*€ 
Sun, as two other Caufes, why Comets may now and then^ ef- 
pecially about the beginning and end of their appearance.fome- 
what digrefs from their (height courfe. Where he alkdges 3 
that he hath much laboured to give an account of Comets by a 
Circular motion, but could not poflibly fatisfie himfelfe in it , 
nor anfvterthe Phenomena of moft,though perhaps that Hypothecs 
may ferve to falve fome of them. 
But then, to explaine tfeat Trajectory rettilinear motion, he 
fubje&s the Comet of A, 165 to a very rigid calculus, to (hew, 
how that line is to be delineated, and how that way is applicable 
to all other Comers, 
Further, to render a Caufs of this motion, he fuppofeth,thar, 
as allCeleftial Bodies move about their Axes, their Atmofphere 
wheeling perpetually round about with them $ fo the matter 5 
Xxxx 2 which 
