L O N D O N S O C I E T " F O R P R O M O T I N G C H R I S T I A N K N O W L E D G E N EW "O RK : TH E MACM ILL AN CO M PAN" CO NT ENT S PART I G RE E K AS T RO NO M " T O A RIS TARC H US T HALE S ANA"I M A NDER ANA"I M EN E S P"THAG ORA S PAR M ENI DE S ANA"A G O RA S E M PED OC LE S TH E P"THAG OREAN S (E N OP ID E S O F (am o s PLAT O E O" S CALL IPP S A R IST OTLE UD U , U , H E RA C LID E S O F PON S TU . PART II ARIS TARC H US O F SA M O S TH E HELIOCE NTR IC H"POTH ES I S O N T H E APPARE NT DIA M ETE R O F T H E S UN O N TH E S I Z E S AND DIST AN C E S O F T H E S UN AND M O O N O N T H E "EAR AND “ G R EAT "E AR ’ L ATER I M PR OVEM E NT S O N ARI STARC H US S FIG URE S B IB LI OG RAPH" C HRO NOLO G" PA RT I. H GREEK ASTRONOMY TO ARISTARC US . T HE title - page of this bo ok necessarily bears the name o f e o r o n man but the reader will find in its pages the story , part of the story, of many other Pioneers Of Progress . The crowning achievem ent Of anticipating the hypothesis Of Copernicus belongs to Aristarchus Of Samos alone ; but to see it in its proper setting it is necessary to have f o f ollowed in the footsteps the earlier pioneers who, by l one bold specu ation after another, brought the solution one of the problem nearer, though no before Aristarchus actually hit upon the truth . Thi s is why the writer has thought it useful to prefix to his account Of Aristarchus a short sketch Of the history o f the development o f ’ astronomy in Greece down to Aristarchus s time , which i s indeed the most fascinating portion o f the sto ry o f Greek astronomy . The extraordin a ry advance in astronomy made by the . Greeks in a period o f little more than three centuries t is a wor hy parallel to the rapid development , in thei r O f hands , pure geometry, which , created by them as a theoretical science about the same time, had by the time ’ o fA ri sta rchu s covered the ground Ofthe Elements (includ ing solid geometry and the geometry of the sphere) , had o f established the main properties the three conic sections , had solved problems which were beyond the geometry of o f the straight line and circle , and finally, before the end 2 ARISTARCH US OF SAMOS ' eh r E C thethird é €uy . had been carried to its highest ' er e i n J eni s p f c t p by the g u of Archimedes , who measured the areas OI curves and the surfaces and volumes o f curved surfaces by geometrical methods practically anti ci pa ting the integral calcul us . To understand how all this was possible we have to - remember that the Greeks , pre eminently among all the O f nations the world , possessed just those gifts which are essential to the initiation and development of philosophy and science. They had in the first place a remarkable power of accurate observation ; and to this were added s clearnes Of intellect to see things as they are , a passion o f fo r a nd ate love knowledge its own sake , a genius for speculation which stands unrivalled to this day. Nothing that is perceptible to the senses seems to have escaped them ; and when the apparent facts had been accurately w/z ascertained , they wanted to know the y and the where ore f , never resting satisfied until they had given a x rational e planation , or what seemed to them to be such , o r x o f the phenomena observed . O bservation e periment SO and theory went hand in hand . it was that they developed such subjects as medicine and astronomy . In h astronomy t eir guiding principle was , in their own ex ” pressive words , to save the phenomena This meant that , as more and more facts became known , their theories . were, continually revised to fit them It would be easy to multiply instances ; it must o ne suffice in this place to mention , which illustrates not only the certainty with which the Greeks detected the f occurrence o even the rarest phenomena , but also the persistence with which they sought for the true ex planation . med s A D . s Cleo e (second century . ) mention that there “ were stories o f e xtraordinary eclipses which the more ancient o f the mathematicians had vainly tried to GREEK ASTRONOMY TO \ ARISTARCH US 3 “ explain ; the supposed paradoxical case was that in “ to which , while the sun seems be still above the western i d o r z ecl se t . ho i on , the p moon i s seen rise in the east The phenomenon appeared to be inconsistent with the explanation o f lunar eclipses by the entry o f. the mOo n ’ into the earth s shadow ; how could this be i f both bodies were above the hori z on at the same time ? The ” “ more ancient mathematicians essayed a geometrical explanation ; they tried to argue that it was possible that a spectator standing o n an emi nence o f the spherical f e o cone L . earth might see along the generators a , a little downwards o n all sides instead o f merely in the o f plane the horizon , and so might see both the sun and ’ the moon even when the latter was i n the earth s leo med es shadow . C denies this and prefers to regard the whole story Of such cases as a fiction designed merely fo r the purpose Of plaguing astronomers and philosophers no a no m a thema Chald ean , he says , Egyptian , and no o r ticlan philosopher has recorded such a case . But the phenomenon is possible, and it is certain that it had been observed in Greece and that the Greek astronomers did no t rest until they had found o ut the solution of the z z fo r Cleo med es x pu le ; himself gives the e planation , namely that the phenomenon is due to atmospheric re f fraction . O bserving that such cases O atmospheric refraction were especially noticeable in the neighbour O f Cleo m ed es on hood the Black Sea , goes to say that it is possible that the visual rays going o ut from o u r eyes o n are refracted through falling wet and damp air, and so reach the sun although it is already below the horizon and he compares the well - known experiment o f the ring o f o u t O f at the bottom a jug, where the ring, just sight V when the jug is empty, is brought into iew when water is poured in . o f a wa s The genius the race being wh t it , the Greeks 4 ARISTARCH US OF SAMOS must from the earliest times have been in the habit of scanning the heavens, and, as might be expected , we find the beginnings of astronomical knowledge in the earliest Greek literature . In the H omeric poems and in Hesiod the earth is a n O flat circular disc ; round this disc ru s the river ceanus , encircling the earth and flowing back into itsel f. The o f flat earth has above it the vault heaven , like a sort o f hemispherical dome exactly covering it ; this vault remains for ever in one position ; the sun , moon and O the stars move round under it, rising from ceanus in east and plunging into it again in the west . Homer mentions, in addition to the sun and moon , the Morning Star , the Evening Star, the Pleiades , the H O “ yades , rion , the Great Bear ( which is also called by o f l - B o Otes the name the Wain Sirius , the ate setting i e , . , (the ploughman driving the , Wain) Arcturus as it s f H was fir t called by Hesiod . O the Great Bear omer says that it turns round o n the same spot and watches ’ i e O rion ; it alone is without lot in O ceanus s bath ( . o to it never sets) . With regard t the last statement it is be noted that some of the principal stars O f the Great in e. Bear do now set in the Mediterranean , g . places R further south than hodes (lat . y , the hind foot , o f x and the tip the tail , and at Ale andria all the x a . seven stars e cept , the head It might be supposed ” that here was a case of H omer nodding B ut no ; the Old poet was perfectly right the difference between the facts as Observed by him a nd as seen by us respectively o f is due to the Precession the Equinoxes , the gradual movement o f the fixed stars them selves about the pole Of H the ecliptic, which was discovered by ipparchus (second B century C ) .