If the magnetic variation has been determined for the region, we may use a map. Such a map as that shown below 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 11½° to the west; in 1844 of 8½° 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 variation closely approximating 4½° 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, provided always that there is no local magnetic attraction. If we are not fortunate enough to possess such a map, the methods previously referred to for obtaining the astronomical north must be employed; observing the direction in which the sun culminates at noon will give us the south point astronomically; from observations of the pole star at night the astronomical north can also be determined. From the former of these observations the magnetic variation is obtained without any difficulty, even in the absence of accurate local time. When this is available other methods are applicable. It is sad to think how much time is lost in the investigation of a great many of these questions for the reason that the published observations were made only with reference 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 with minute accuracy in all cases, either by the French or Prussian Commissions to which I have referred, it is perfectly certain that the solstitial orientation of Karnak and other temples, which I shall have to mention, would have been long ago known to all scholars. CHAPTER VIII. THE EARLIEST SOLAR SHRINES IN EGYPT. Not only can an inquiry like that referred to in the previous chapter be prosecuted--_it has been prosecuted_. 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 Commission which accompanied the army, a Commission appointed 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 south as Philæ.