August 27, 1908] 



NA TURE 



391 



5!7i?r£i7iYG FOR ARCH.EOLOGISTS. 

 1. 



Al/'E have now two societies for the astronomical 

 • ' study of ancient monuments at worlc in 

 Britain ; a considerable number of tlie monuments have 

 already been astronomically surveyed, with the result 

 that the various aliyjnments indicated have been shown 

 to have been laid out to facilitate and utilise observa- 

 tions of the sun or stars. 



It is not to be wondered at, therefore, that I have 

 been repeatedly asked, now in one region, now in 

 another, to put on paper some general hints to those 

 who may feel inclined to take up the work so as to 

 secure the necessary observations. 



I think the first useful thing to say is that the 

 inquiry is much less complex, and takes much less 

 time in the measurement of any one monument, than 

 is generally imagined ; that the ideas involved are 

 very simple, and do not go beyond the knowledge 

 which should be possessed by everybody who wishes 

 to enjoy arid understand something of the world 

 around him. 



In the first place, the astronomical side of the in- 

 quiry, so far as the monuments are concerned, is very 

 restricted. It has little to do with the various data 

 concerning them which arclijeologists, with W'onderful 

 diligence, have now been accumulating for several 

 centuries. The weight, shapes, size, colour and 

 nature of the stones are not in question. All use 

 of the spade for finding treasure or anything else is 

 not in our province. If, when plans are given, the 

 relation of the stones to each other is accurately given, 

 we can accept them so far as the arrangement of 

 the stones inter se is concerned. 



One great advantage of being freed from the neces- 

 sity of doing all this work is that would-be inquirers 

 are saved the e.xpenditure of a great deal of time and 

 money ; to them the spade is needless, because they 

 •deal only with the relation of the monument to the 

 surrounding surface, and for the same reason the 

 conditions of the stones themselves are indifferent to 

 them. 



What, then, is it they have to do? They have 

 simply to determine, with an accuracy as great as can 

 be achieved by the instruments at their disposal, the 

 line of direction indicated by the lie of the stones in 

 the various monuments. This problem is at its 

 simplest in the case of the so-called " Avenues," such 

 as those at Challacombe and Merrlvale, on Dartmoor. 

 Do they lie east and west, or north and south, or 

 in any other intermediate direction? 



Again, take the cases of the so-called " outstand- 

 ing " stones or tumuli so often met with at some 

 distance outside the Cornish circles — those of the Merry 

 Maidens and Tregaseal, to give instances; do they lie 

 to the east, or the west, or the north or the south, oi 

 at some intermediate angle? and at what angle? 



In the case of cromlechs or dolmens the matter 

 is not quite so simple, except in the case of those 

 furnished with an obvious outlook, an aiye ouvcrte 

 or couverte, to adopt the terms employed by French 

 archreologists. I suppose tliere are hundreds of 

 monuments of this class, of which so-called " plans " 

 exist, but in spite of these plans, which may be quite 

 good so far as the interrelation of the stones is con- 

 cerned, we have no certain knowledge as to the exacf 

 direction in which these alley-ways or creeps point. 

 The stones have been dealt with as stones, and their 

 relations to their surroundings have been entirely 

 neglected. 



Fundamentally, then, to get out of this impasse it 

 is a question of these directions in the first instance. 

 NO. 2026, VOL. 78] 



How is this to be done? It is here that the elements 

 of knowledge of the things around us, which, I am 

 thankful to say, now form part of the teaching in 

 our best elementary schools, and which, therefore, are 

 not of a very recondite nature, come in. 



The ancient monuments, like everything else on 

 the face of the earth or sea, appear to anyone who 

 examines them close at hand to occupy the centre of 

 a plane, which is really the little bit of the surface of 

 the earth that we can see from any one point of view. 

 This circular patch of land or sea is bounded in every 

 direction by what is called the horizon, whicli is the 

 most distant part of the land or sea from us, and on 

 which the sky seems to rest. In the case of the sea, 

 this horizon is level all round. In the case of the 

 land, it ma)" be high or low according to the sur- 

 rounding conditions. If we live in a street it is high, 

 its height depending upon the number of storeys in 

 the opposite houses; if we are on the heights of 

 Dartmoor it is very low, almost as low as a sea 

 horizon, and as sensibly circular. 



Suppose us, then, surrounded by this circular hori- 

 zon, in front of an avenue ; how, when we have 

 rr^easured the stones and plotted them at the proper 

 distances apart, can we indicate the general direction 

 of the lines of stones? We can divide the circle of 

 the horizon, like all other circles, into 360°. But where 

 — in what direction — are we to begin the numbering? 

 Where must the zero be? 



All mankind has now agreed for hundreds of years 

 that the zero must be the north point; opposite to it is 

 the south point, and the line joining these north and 

 south points is called a meridian line. 



This meridian line, passing along the earth's surface 

 and joining the north and south points of the horizon, 

 lies in a vertical plane passing through the point over- 

 head called the zenith. The term meridian is used 

 because the sun passes through this plane at the 

 middle of each day. The line at right angles to the 

 meridian line passes through two points on the horizon 

 midway between north and south. These are called 

 the east and west points, and in the four points now 

 named we have the so-called cardinal points on the 

 horizon. 



The meridian so defined is called the astronomical 

 meridian, and the cardinal points of the horizon in- 

 volved are called astronomical or true. 



The astronomical north and all the other points 

 are absolutely stable ; they never vary, and are always 

 the same at all places. This north point may be 

 roughly found at night, as it is the point of the horizon 

 under the pole-star, the star which nearly occupies 

 the centre of the circle round which tlie stars revolve 

 in their daily apparent movement. The south point 

 may be defined as the point of the horizon under 

 the sun at noon. 



Now all this seems plain sailing, but the trouble of 

 it is that there are two north points and two meridians 

 to be considered. 



If we take a magnetic needle and balance it hori- 

 zontally on a vertical pivot, its ends will be directed 

 to two points on the horizon, which are not the same 

 at all places with regard to the cardinal points. By 

 drawing a great circle through these two points and 

 the zenith point of the place, we obtain the plane of 

 the magnetic meridian. The magnetic needle, as we 

 see it in a pocket compass, has a marked N. end, and 

 its length lies in and defines the magnetic meridian. 



The magnetic meridian line is the intersection of 

 the plane of the magnetic meridian with the plane of 

 the horizon. 



In Britain these two meridians do not coincide; at 

 present, on the average, they form an angle with each 



