( 6i5C ) 
Parabolical line, are in power equal to a Series (5f Squares increafed 
by aferies of Equals, fuppofe + : Ani(prop,^$,^i,Comc,Se5l.) 
that c the Ordinates to the Conjugate Diameter of an Hyperbola, 
(that is, the particles of which that Hyperbolical fpace confift^,) aire 
foalfo, ^'/^♦y:^T^+~h* .• f where >^,7',L, are permanent quantities, 
and taken fucceffively in Progrefiion Arithmetical ;)Itwaseafie 
(fovMMeuraet, otM.Hpigens, ox: any other,) to infer. That, if we 
can Redifie the one, we may Square the other, & vice verfa But from 
whence foever M.H^/^r4<f^ had it 5 we may, as before, reafon^ibly con- 
clude, that Mr;.iV<?// had it before him. V AndM. H^^<?^^ is apcrfonof 
that ingenuity, that, when he fliall better confider of it,he WillCI doubt 
not) be of the fame mind. London, 0B.%.i6Tl% 
The other Letter is of Sr .ChriftopherWrenlO.i'^rz/^jor General of hisMa- 
jeflies Bnildings^ &c, 
SIR, 
THatldid, in the year 1658. find a i^fm^k line equal to that of a 
Cycloid, and the parts thereof, was then very well known, not 
in England only, but in France and Holland, And 1 have not yet heard 
of any, who do pretend to have known it, before I difcoverM it ; 
which was the fame year acknowledged in Print by thofe of France, 
But I do not pretend to havebeenthe^^r^ that did ever find a Streighc 
line equal to a Crooked . For I very well know, that Mr. fvilliam Neil 
had, the year before, found out and demonftrated. How to cpnftruci 
a Crooked line fo as to be equal to a Streight, by a certain feries of 
Numbers after the method oiDt.Wallis, And though He did not there« 
indemonftrate the other properties of that Line 5 yet the fame were 
prefently after demonftrated by my felf and others, and the nature of 
the Line fully difcover'd , being a certain Paraioketd, And that 
which M. /fif^i^r^^ is faid afterwards to have found out, in th^ ye^r 
165^, and U.Fermap in the year i6t5o, are but the fame with that- 
of Mr.Neik. 
An Accompt 
