NATURE 



[May 7, 1891 



W^ 



ON SOME POINTS IN THE EARLY HISTORY 

 OF ASTRONOMY} 



II. 



E have next to deal with the astronomical relations 

 of the horizon of any place, in connection with the 

 worship of the sun and stars at the times of rising or setting, 

 when of course they are on or near the horizon ; and in 

 order to bring this matter nearer to the ancient monuments, 

 we will study this question for Thebes, where they exist in 

 greatest number and have been most accurately described. 

 The French and Prussian Governments have vied with 

 each other in the honourable rivalry of mapping and 

 describing the monuments. The French went to Egypt 

 at the end of the last century, while the Scientific Com- 

 mission which accompanied the army, a Commission ap- 

 pointed by the Institute of France, published a series of 

 volumes containing plans of all the chief temples in the 

 valley of the Nile, as far as Philae. 



In the year 1844, after ChampoUion had led the way in 

 deciphering the hieroglyphics, we became almost equally 

 indebted to the Prussian Government, who also sent out 

 a Commission to Egypt, under Lepsius, which equalled 

 the French one in the importance of the results of the ex- 

 ploration ; in the care with which the observations were 

 made, and in the perfection with which they were 

 recorded. Hence it is that in attempting to get informa- 

 tion from ancient temples it is wise to study the region 

 round Thebes, where the information is so abundant and 

 is ready to our hand. 



We have then to consider an observer on the Nile at 

 Thebes, and to adjust things properly we mubt rectify 

 the globe to the latitude of 25° 40', or, in other words, 

 incline the axis of the globe at that angle to the wooden 

 horizon. 



. It will be at once seen that the inclination of the axis to 

 the horizon is very much less than in the case of London. 

 Since all the stars which pass between the Norih Pole 

 and the horizon cannot set, all their apparent move- 

 ment will take place above the horizon. All the stars 

 between the horizon and the South Pole will never rise. 

 Hence, stars within the distance of 25° from the North 

 Pole will never set at Thebes, and those stars within 25° 

 of the South Pole will never be visible there. At any 

 place the latitude and the elevation of the pole are the 

 same. It so happens that all these places with which 

 archaeologists have to do in studying the history of early 

 peoples, Chaldsea, Egypt, Babylonia, China, Greece, &c., 

 are all in middle latitudes, therefore we have to deal with 

 bodies in the skies which do set and bodies which do not, 

 and the elevation of the pole is neither very great nor 

 very small. In each different latitude the inclmation of 

 the equator to the horizon as well as the elevation of the 

 pole will vary, but there will bi a strict relationship 

 between the inclination of the equator at each point and 

 the elevation of the pole. Except at the poles themselves 

 the equator will cut the horizon due east and due west. 

 Therefore everything to the north of the equator which 

 rises or sets will cut the horizon between the east or west 

 point and the north point ; those bodies which do not set 

 will of course not cut the horizon at all. 



The sun and stars near the equator, in such a latitude 

 as that of Thebes, will appear to rise or set at no very 

 considerable angle from the vertical ; but when we deal 

 with stars rising or setting near to the north or south 



' From shorthand notes of a course of lectures to working men delivered 

 at the Mus2umof Practical Geology, Jtrmyu Street, in N.-vember i8go. 

 The notes were revised by me at As*an during the month of January. I 

 have found, since my return from Egypt m March, that part of the subject- 

 matter of the lectures has been previously discussed by Herr Nisscn, who 

 has employed the same materials as myself. To him, therefore, so far as 

 I at present know, belongs the credit of having first made the suggestion 

 that ancient temples were oriented on an astronomical basis. His article is 

 to be found in the Rheinisches Mitseuiti /fir PhiloCogie, iZi^. Continued 

 rom vol. xliii. p. 563. 



NO. I 123. VOL 44] 



points of the horizon they will seem to skim along the 

 horizon instead of rising directly. 



Now it will at once be obvious that there must be a 

 strict law connecting the position of the sun or a star 

 with its place of rising or setting. Stars at the same 

 distance from the celestial pole or equator will rise or set 

 at the same point of the horizon, and if a star does not 

 change its place in the heavens it will always rise or set 

 in the same place. Here it will be convenient to intro- 

 duce one or two technical terms : we generally define a 

 star's place by giving, as one ordinate, its distance in 

 degrees from the equator: this distance is called its dech- 

 nation. Further, we generally define points on the 

 horizon by dividing its whole circumference into 360°, 

 so that we can have azii7tuths of 90° from each pole to 

 the east and west points. We also have amplitudes from 

 the east and west points towards each pole. We can 

 say then that a star of a certain declination will rise or 

 set at such an azimuth ; or at such an amplitude. This 

 will apply to both north and south declinations. 



The following table gives the amplitudes of rising or 

 setting (north or south) of celestial bodies having declina- 

 tions from o' to 64° ; bodies \yith higher declinations than 

 64° never set at Thebes if they are north, or never rise if 

 they are south, as the latitude (and therefore the elevation 

 of the pole) there is nearly 26°. 



This being premised, we now pass to the yearly path 

 of the sun, with a view of studying the relation of the 

 various points of the horizon occupied by the sun at 

 different times in the year. In the very early obser- 

 vations that were made in Egypt, Chaldaea, and else- 

 where, when the sun was considered to be a god who 

 every morning got into his boat and floated across space, 

 there was no particular reason for considering the ampli- 

 tude at which the boat left, or came to, shore. But a few 

 centuries showed that this rising or setting of the sun in 

 widely varying amplitudes at different parts of the year 



