(^89) 
moon, the Moon at C, the Earth ate, A^arswiWhe feenat % 
its true place,as if the Earth were atT. But th€n,after the Full, 
the Moon at D,the Earth at d ; Mars will be feen^ not at 7, but 
at^j too forward : and yet more^ when the Mooa (atthelaft 
Quarter ) is at E, the Earth at e, and Mars feen at e. If there- 
tore. M^r/ (wheninoppofirion to theSun) be found (all other 
allowances being made ) fomewhat too backward before the 
Full moon, and fomewhat too forward after the Full-moonj 
(and moft of all^at the Quadratures ) it will be the beft con« 
firmation of the Hypothcfi?. ( The like may be fitted to JUars 
in otherpofitions, mutatis mutandis and lb for the other Pla- 
nets.) 
But this proof, is of like nature as that of the Parallaxis of 
the Earths Annua! Orb to prove the Copernican Hypothefis, 
If it can be obferved, It proves the Affirmative / butif it cannot 
be obrerved,it doth not convince the Negative^but only proves 
that the Seraidiameter of the Earths Epicycle is fo fmali as not 
to make any difceroable Parallax. And indeed, I doubt , that 
will be the iflue. For the Seraidiaraeter of this Epicycle^being 
little more than the Seraidiameter of the Earth it felf, or about 
if thereof (as is conjectured, in the Hypothefis ^ from the Mag- 
nitudes and Diftances of the Earth and Moon compared;) and 
there having not as yet bsen ©bferved any difcernable Farallax 
oiMars, even in his neereft poficion to the Earth; it is very 
fufpicious, thac here it may prove fo too* And whether any of 
the other Planets -will be more favourable in this point^l can- 
not fay. 
, JNntADVE\SlONS 
of Dr. Walh's, upoji MrHobs's late BooJ{, DePrincipiis & 
Ratiocinatione Geometrarum* 
"'Thefe were communicated by way of LettefjWritten inOX" 
fQrd^]\i\y 24, 1666. to an Acquaintance of the Autlmvy asfoi« 
lows : 
Since I faw you laft^I have read ove%^r. Hohs% Book Cmtra 
Geometras(pv De Frincifnis ^§ 'Ratiocinatione GeometrBrumjwhich 
you then fliewed me. A Ner^? Book of Old mauer : Containing 
but a Repetition of what he had before told us.more than once ; 
jand which hath been Anlwered long agoe. 
■ In which, though there be Faults enough to offer ample mat- 
Qq :? tcr 
