May 21, 1891J 



NATURE 



57 



w 



ON SOME POINTS IN THE EARLY HISTORY 

 OF ASTRONOMY.^ 



III. 

 E now come to the important point for our present 

 inquiry — the direction m which the temple is built, 

 or, technically, its orientation. Confining ourselves for the 

 moment to Karnak, is there any meaning in the direction 

 of that line, some 500 yards long, which is obviously the 

 main feature of the building, and to which all parts are 

 accessories ? 



How can we instrumentally determine this? I have 

 the necessary apparatus here, and the question may be 

 answered in a few minutes ; we have simply to determine 

 either the azimuth or the amplitude (and as we have 

 seen one of these gives the other) of the point of the 

 horizon towards which this long line is directed. 



The azimuth compass is an instrument familiar to 

 most of you. It consists of a magnetic needle fastened 



Fig. II. — Azimuih compass, sv, direction pointer ; m, sun shade (for 



observations of sun) ; i, reading prism ; a b, graduated card with attached 



compass-needle. 



to a card carrying a circle divided into 360°, which can 

 be conveniently read by a prism when the instrument is 

 turned toward any definite direction marked by a vertical 

 wire. 



A theodolite armed with a delicately hung magnetic 

 needle which can be rotated on a vertical axis will do 

 equally well ; it has first of all to be levelled ; there is a 

 little telescope with which we can see along the line. 



Fig. 12. — Compass theodolite and tripod. 



When we wish, for instance, to observe the amplitude of 

 a temple, the theodolite is set up on its tripod in such a 

 position that we can look along the temple wall or line 

 of columns, &c., by means of the telescope. We then 

 get a magnetic reading of the direction, after having un- 

 damped the compass ; the compass showing the angle 

 made between the line and the magnetic north (or south), 

 as in the azimuth compass. 



Having made such an observation as that I have de- 



' Continued'from p. ii. 

 NO. II 25, VOL. 44] 



scribed, the next thing we have to do is to determine 

 astronomically the real north, which is the only thing 

 of value. There are two ways of getting this astronomical 

 bearing or azimuth. 



It is sad to think how much time has been lost in the 

 investigation of a great many of these questions, for the 

 reason that the observations were made only with refer- 

 ence to the magnetic north, which is vastly different at 

 different places, and is always varying ; few indeed have 

 tried to get at the astronomical conditions of the problem. 

 Had this been done either by the French or Prussian 

 Commissions to which I have referred, it is perfectly 

 certain that years ago the solstitial orientation of Karnak 

 and other temples which I shall have to demonstrate ta 

 you would have been long known to all scholars. 



If the magnetic variation has been determined for the 

 region we may use a map. Such a map as that shown in 

 Fig. 13 gives us the lines along which in the British Isles 

 the compass variation west of north reaches certain values. 

 From such a map for Egypt we learn that in 1798 a magnet 

 swung along a line extending from a little to the west 

 of Cairo to the second cataract would have had a variation 

 of 12° to the west ; in 1844 of 8^ to the west ; and at the 

 present time the variation is such that observations made 

 along the same part of the Nile valley will have a varia- 

 tion closely approximating 5° to the west. By means of 

 such a map it is quite possible to get approximately the 

 astronomical bearings of all temples which were observed 

 by the French in 1798 or by the Germans in 1844, or 

 which can be observed in the present day. 



If we are not fortunate enough to possess such a map^ 

 the theodolite will enable us to observe the direction in 

 which the sun culminates at noon. This gives us the 

 south point astronomically. From observations of the 

 pole star at night, the astronomical north can be deter- 

 mined. From either of these observations the magnetic 

 variation is obtained without any difficulty. 



This being premised about the method, we next come 

 to the results. The amplitude of the point to which the 

 axis of the great temple at Karnak points is 26° N. of 

 W., which we learn fcom the table already given is pre- 

 cisely the amplitude of the place of sunset at the summer 

 solstice. The amplitude of the point to which the axis 

 of the small temple points is 26° S. of E., e.xactly the 

 position of sunrise at the winter solstice. 



There is more evidence of this kind. Abydos, 

 one of the oldest temples in Egypt, built, accord- 

 ing to tradition, by the servants of Hor, is now, 

 it is true, a heap of ruins, the brick walls best 

 showing its direction ; but it is possible to 

 gather the orientation of it by these guiding 

 lines. It is 27° N. of W. — as it should be, being 

 in a higher latitude than Karnak — and evidently 

 was oriented to the solstice. 



At Abydos, then, as at Karnak, we get exactly, 

 within a degree, the amplitude shown in the 

 tables for the sun in the Nile valley at sunset at 

 the summer solstice. So that the Egyptians 

 who were employed in building those temples 

 must have known exactly what they were gomg 

 to do, and what they did was to build a temple 

 such that the sun at setting should, at the 

 summer solstice, pour its light along the axis 

 of the temple. If Maspero and the great 

 authorities in Egyptian archaeology are right — namely, 

 that the Abydos temple was founded before 4000 B.C. 

 — and if we can depend upon the French figures, we 

 are driven to the conclusion that we have in this temple 

 a building which was orientated to the solstitial sunset 

 place in the valley of the Nile. The Nile valley holds 

 other solar temples besides those we have named, but it 

 is best to fully study Karnak ; instead of being a mere 

 heap, the orientation of which is obtainable only by the 

 general lie of the remains, this temple is still in such 



