(If 5 ) 
ionfider-s the principal Obfervations, hitherto made of the Mo- 
tion of the Planets and the Fixed Stars * of their Magnitude, 
Figure , and other Accidents 5 drawing thence feveral Conclufr- 
ons 5 in which he eftablifhes his Hypothecs, The Second contains 
his Agronomical Tables , made according to the Hypothefes, of 
the Firft Part 3 together with Inftrudions teaching the manner 
of ufing them. 
Thirdly ,That Aftronomers will find in this Book many very re- 
markable things 3 concerning the Apparent Diameter of the Sm 
and the other Stars , the Motion of the Libration of the Moon > 
the Eclipfes , Parallaxes , and Refractions : And that this Author 
fhews 3 that there is a great difference between Optical and Agro- 
nomical Refradion, which Tycho and many others have confounded^ 
undertaking to prove,that, whereas thefe Aflronomershme believed, 
that the remoter any Star is , the lefs is its Refradion 9 on the con- 
trary the Refradion is the greater , the more a Star is difhnt e 
And among many other things, he ingenioufly explicates the 
two contary Motions of the Sun , from Eaft to Well , and 
vice verfa > by one onely Motion upon a Spiral turning about 
a Cone. 
Fourthly , That he reprefents, How uneafie it is toeftablifh 
fure Principles of this Science, byreafonof the difficulties of ma- 
king exad Obfervations. So , for example , in the Obfervation 
of the Equinox, every one is miftaken by fo many Hours , as he 
is of Minutes , in the Elevation of the Pole , or the Diameter of 
the Sun , or the Refradion , or in any other circumfhnce. In the 
Obfervation of the S olflice , the error of one only Second caufeth 
a miftake of an Hour and an half : mean time ’tis almoft impoffible 
to avoid the error of a , Seconds and even the fharpeft fight will 
not be able to perceive it, except it be affifted with an Inftrument 
of a prodigious bignefs. For to mark Seconds , though Lines 
were drawn asfubtil as the (ingle threds of a Silk-worms Clew 5 
(which are the fmalleft fpaces to be djfcerned by the iharpeft 
Eye ) by the Calculation made by this Author there would need 
an Infkument of 48. feet Radius , fince Experience fhews , that 
there needs no more at mod, than 3600. threds of Silk to cover 
the fpace of an inch . But , fuppofe one could have a Quadrant 
or this bignefs , who can affure himfelf , that dividing it into 
Fff 2 3240003 
