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An Extract 
©fa Letter mitten Decemb. 28. 1 666. by M, Auzout to the 
Publijher , concerning away of his , for taking the Diameters 
of the Planets , and for knowing the Parallax of the Moon 5 
as alfo the-Reafon , why in the Solar Eclipfe above calculated 
the Diameter of the Moon did increafe about the end, 
I did apply my felf the laft Summer to the taking of the Dia- 
meters oi the Sun, Moon , and the other Planets , by a Method, 
which one M* Picard and my felf have, efteem’d by Us the belt of 
all thofe 3 that have been pra&is’d hitherto 5 ffnce we can take the 
Diameters to Second Minutes , being able to divide one foot into 
24000, or 30000. parts, fcarce failing as much as in one only 
part 3 fo as we can in a manner be affurd , not to deceive our 
lelvesin 3. or 4 .feconds^ I.fhall not now tell you my Obferyati- 
ons,but 1 may very well affure you, that the Diameter of the Sun 
has not been much lefs in. his Apogee , than 3i.m. 37. or 40. fee, 
and certainly not leffe than 3 1 .m. 3 5. fee. and that at prefent in his 
Rerigee it paffes not 32. m. 45. fee. and may be leffe by a fecond or 
two. That, which is at the prefent troublefome,is, that the Vertical 
Diameter, which is the mofteafie to take, isdiminifht, even at 
Noonjoy 8 . orp. fee, becaufe of the Refractions , which are much 
greater in Winter than Summer at the fame height *, and that the 
Horizontal Diameter is difficult, becaufe of the fwift motion, of 
the Heavens. 
As for the Moony I never yet found her Diameter lefs. than 
29. m. 44. or 45, fee. andlhavenotfeenitpafs 3 3. m. orif.it hath, 
it was only by a few feconds. But I have not yet taken her in all the 
kinds of foliations of the Apogees and Perigees which happen, with 
the Conjunctions and Quadratures. Ido not mention all,what can 
be deduced from thence , but if you have Perfons at London , that 
obferve thefe Diameters ,, we may entertain our felves more about 
this Subjedh, another time. I foall only tell you, that I have found 
a Way to know the Far ad ax of the Moon , by the means pf her 
Diameter : Fid. if on a day, when (he is to be in her Apogee or Pe- 
rigee , and in the moffc BorealSlgnts , you take her Diameter to- 
wards the Horizon^ and t|en, towards the South) with her Altitudes. 
above 
