The Universe, Wrought For Us By A

Yet The Widespread Planetary Theories, Advanced By Ptolemy And Most Other Astronomers, Although Consistent With The Numerical Data, Seemed Likewise To Present No Small Difficulty. For These Theories Were Not Adequate Unless They Also Conceived Certain Equalizing Circles, Which Made The Planet Appear To Move At All Times With Uniform Velocity Neither On Its Deferent Sphere Nor About Its Own Epicycle's Center.

Therefore, Having Obtained The Opportunity From These Sources, I Too Began To Consider The Mobility Of The Earth.

Since, Then, There Is No Objection To The Mobility Of The Earth, I Think It Must Now Be Considered Whether Several Motions Are Appropriate For It, So That It Can Be Regarded As One Of The Wandering Stars. For The Fact That It Is Not The Centre Of All Revolutions Is Made Clear By The Apparent Irregular Motion Of The Wandering Stars, And Their Variable Distances From The Earth, Which Cannot Be Understood In A Circle Having The Same Centre As The Earth.

So Far As Hypotheses Are Concerned, Let No One Expect Anything Certain From Astronomy, Which Cannot Furnish It, Lest He Accept As The Truth Ideas Conceived For Another Purpose, And Depart From This Study A Greater Fool Than When He Entered It.

Among The Authorities It Is Generally Agreed That The Earth Is At Rest In The Middle Of The Universe, And They Regard It As Inconceivable And Even Ridiculous To Hold The Opposite Opinion. However, If We Consider It More Closely The Question Will Be Seen To Be Still Unsettled, And So Decidedly Not To Be Despised. For Every Apparent Change In Respect Of Position Is Due To Motion Of The Object Observed, Or Of The Observer, Or Indeed To An Unequal Change Of Both.