(373) 
An Extract 
of a Letter written Hectmh, 28. 1666. bj kvii(mtt$the 
Puhlifher , concerning a rvaj of his y for taking the Diameters 
of theV\^Vitx.% ^ md for knowing Parallax ^/ Moon 5 
as alfo the Reajon 5 whj in the Solar Eclipfe above calculated^ 
the Diameter of the Moon did increafe about the end* 
I did apply my felf the laft Sumraer to the taking of the Dia^ 
meters oi the Sun, Moon, and the other Planets, byaMethodg 
which one M, Picard and my felf have, efteem^d by Us thebeft of 
allthofe^ that have been pradis'd hitherto 5 fince we can take the 
Diameters to Second Minutes , being able to divide one foot into 
24000. or 30000. parts 5 fcarce failing as much as in one only 
pwart 5 fo as we can in a manner be affurd , not to deceive our 
felvesin 3. or ^,feconds, I fliall not now tell you my Obfervati- 
onsjbut 1 may very well afliire you, that the Diameter of the Sun 
has not been much lefs in his Apogee^ than ji.ra. 37. or 40. fec<, 
and certainly not lefle than 31^0. 35. fee. and that at prefent in his 
Pot^^^ it pafles not 32. m. 45. fee. andmay beleflfebyafecondor 
two^That^whichisat the prefent troublefome^is, that t\iQ Vertical 
Diameter , which is the moft eafie to take , is diminiflit ^ even ar 
Noouyhy 8 . or p. fee. becaufe of iht Refractions , which wirem.uch 
greater in Winter than Summer at the fame height ^ and that the 
Horizontal D'mmm is difficult, becaufe of the fwift motioii of 
the fieavens. 
As for the Moon , I never yet found her Diameter lefs thm 
29. m. 44. or 45. fee. andlhavenotfeenitpafs 33.m.orif it hath;, 
it was only by a few feconds. But I have not yet taken her in all the 
kindsof fituationsof the J f ogees and Pm^^^^ which happen^with 
the Conjunctions and J^adratures. I do not mention all^ what caa 
be deduced from thence, but if you have Perfons at London^ that 
obferve thefe Diameters , we may entertain our felves moreabouc 
this Subjedp another time. I fhall only tell you^that I have found 
a Way to know the Parallax of the Moon , by the means of her 
Diameter : Vid, If on a day, when flie is to be in her A f ogee or Pe-- 
rigee^ and in the moft BorealSign^s, , you take her Diameter to- 
wards the ^i?r/.c^/?3 and then towards the Smth) mthlm Altitudes 
above 
