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SUNDIALS
HISTORY, THEORY, AND PRACTICE
By René R. J. Rohr, Gabriel Godin Dover Publications, Inc.
Copyright © 1965 Gauthier-Villars
All rights reserved.
ISBN: 978-0-486-15170-0
CHAPTER 1
History of the Sundial
In Europe the beginning of the great human adventure took place amid the frosty surroundings of an ice age. One may try to imagine virgin and raw landscapes, framed by a sky more often gray than sunny, but always bathed in the fresh cool air of early morning; here and there small groups of squat men are seen wandering, men whose primitive looks are suggested to us from Heidelberg to Cromagnon by a meagre array of fossil remains.
From dawn, till dusk these remote ancestors of ours had to fight endlessly for survival, against hunger, cold, and the various perils which a merciless nature put in their path. From dawn till dusk, indeed, because it was the only time reckoning they knew. The rhythm of day and night which had regulated all life on earth for a billion years from the life of the algae to that of the trees and the powerful mammoth was also the rhythm of their life. They have left us nothing to witness this fact, but we know it could not have been otherwise. For thousands of years, the sunrise and the sunset were the only signals for a change in their activity. A remote echo of this elementary state of things reverberates through the Bible where the book of Genesis (1: 5) brings us in its first verses the lapidary sentence:
God called the light Day and the darkness he called Night. And there was evening and there was morning, one day.
Painfully thousands of years went by and man did not perish. Indeed he flourished and suddenly he has in his hand a tool – a poor tool, a stone, a raw or roughly hewn piece of flint. But the man who held it did not know that he as well as the whole of humanity had just taken a decisive step. There were many more steps before the great day came when settled life was established.
Gradually but obscurely, man faced a new need. Every primitive being fears the hidden dangers of darkness. And each time a man had to leave his tent of skins or the huts of his tribe to go to some remote place, he had to be able to determine when he should turn back so that he would not be caught on the way by sunset. Undoubtedly, since he spent his life outside, man developed the habit of watching the daily course of the sun and he had probably learned that he could move away from the group as long as the sun rose but that he had to be on his guard from the moment it started going down. His experience must have followed the progress of his tools. He realized that the shadow of the trees shortened in the first part of each day and that it lengthened later. Certainly the instant of transition between these two movements must have soon played an important role in the slow but progressive organization of his life. It was the first step, hesitant as yet, towards the clock-dominated and hectic life of his remote descendants in the twentieth century.
But can we not go a little further and imagine that primitive man had learned to exploit the changes in the length of his own shadow? Or rather that, as his intelligence sharpened, he had the time, through the years, to think of using a rod of a given length, the shadow of which, when set vertically, could help fix the moment when he should meet a companion equipped, perhaps, with the same instrument.
This instrument would have been the first gnomon – the principle of which was used centuries later, when the peoples around the shores of the Mediterranean erected the first stone obelisks on the great squares of their cities. Museums overflow with all kinds of implements from the Neolithic age: thousands of flaked flints have been found, but a simple little rod, besides being highly perishable, would probably be too plain an object to have attracted attention.
All this, admittedly, is pure conjecture. But, happily, progress is not simultaneous everywhere. Do we not have to help us in this kind of research among the reserves of primitive men in the twentieth century in Australia, Melanesia, and New Guinea, many samples of tribes which have not yet gone beyond the Neolithic age? And observation of their customs tends to support the hypothesis just proposed.
In fact, if the search for positive clues on the measure of time turns out to be so difficult for the early stages of human civilization, the archaeologists who have studied the same problem for the initial eras of history arc in no better position. There is no doubt that the gnomon was the first instrument used for the measurement of time by various peoples and that they used the length of the shadow and not its direction in order to do this. Gnomon is a Greek work meaning "pointer." In contrast with our mechanical watches, it could not be used to delineate an interval or lapse of time, but indicated rather a given moment (figure 1).
The intrinsic simplicity of any apparatus used for this purpose makes its identification among other objects found in an excavation rather difficult. Besides, scholars have been faced with an even more elusive problem since the finds are scarce and thinly spread geographically. They are thus compelled either to rely on written documents or to try to interpret as correctly as possible the purpose of the implements discovered when this purpose seems to be related to their special field of study.
Groping through history with this Ariadne's thread, we learn from the papyri that by about 1450 BC gnomons in the form of obelisks were used in Egypt for the measurement of time and the setting up of calendars. Even earlier, Thutmosis III (1501 to 1448 BC) had carried with him on his trips a portable dial, the nature of which is not known to us; it might have resembled an object found and dated as belonging to the same era and which is the oldest sundial known. This object docs not look at all like a gnomon, although it is constructed on the same principle. It consists of a piece of L-shapcd stone about 30 cm long, supporting on its small end a second stone of the same length, but straight and perpendicular to it. The whole thing was oriented on a horizontal plane as indicated in figure 2, i.e., the long stem of the L-shaped stone was placed opposite the sun. This stem was covered by the shadow of the cross piece and on its surface were etched divisions which indicated the hours, according to the height of the sun. The duration of these hours could not be constant from one day to the next because of the variation of the sun's declination during the course of a year.
The chronological Ariadne's thread which we have proposed to follow brings us from Egypt to China, a thousand years before Christ. According to old documents from this country, the gnomon was commonly used as an instrument for astronomical observations. Not only had the Chinese already succeeded in locating the astronomical meridian with its help, but they had also succeeded in fixing the dates of the solstices and had even calculated the inclination of the ecliptic on the plane of the equator. The value of this inclination is 23° 27' in round numbers; the result obtained in China was 23° 54', a very respectable estimate considering the means used to obtain it. It goes without saying that such work cannot be improvised, so we are justified in thinking that gnomons must have been in use in China from very early times. Let us stress that what we have been discussing here are the first appearances of the gnomon in written records. These records also tell us that astronomical observations were initiated in China in the era of Yao, an emperor shrouded in legend, who lived in the twenty-third century before Christ; it is said that he had two of his astronomers executed because they failed to predict an eclipse of the sun.
The same sources also reveal that the perforated gnomon was known in China from earliest times. The peoples living on the shores of the Mediterranean discovered this instrument and its use much later. Its invention was there attributed to the Arab astronomer Ibn Junis who lived at the end of the tenth century AD.
As the gnomon becomes higher, the determination of time by this means becomes more accurate. But since the sun is not a point but a disc with a certain apparent diameter, the edge of this shadow lacked definition because of the penumbra which surrounded it (figure 3). To overcome this difficulty, the Chinese installed a circular disc, through which a round hole was pierced, on top of the gnomon. The shadow then left on the ground formed a little round spot, the image of the sun, the centre of which could be easily determined (figure 4). Finally, around 500 BC a uniform height for all the Chinese gnomons was prescribed by law under the threat of severe penalties.
The absence of written documents among the other nations does not prohibit the possibility that the gnomon was also known there. Well into this century, for example, we were unaware of the old Egyptian dial of the fifteenth century BC mentioned above.
Among the Hindus, one finds from early times gnomons surrounded by concentric circles which made it easier to determine the true south, i.e., the meridian. We shall return to this technique, for it is still quite widely used. This gnomon was rapidly adopted by other peoples of the period and the term "Hindu circles," by which it is currently designated, leaves no doubt of its origin.
In Mesopotamia, the Babylonians and then the Chaldeans enjoyed a high reputation as astronomers. Herodotus describes in his History (fifth century BC) the annual allotment of lands in Egypt and the knowledge of gcometry derived from it – a knowledge which the Greeks imported into their own country. He says, "the Greeks learned from the Babylonians the use of the polos, of the gnomon, and of the division of the day into twelve parts" (11, 109).
In the very rare references to sundials in the texts of that era, the word polos appears here for the first time. Herodotus seems to make a distinction between the polos and the gnomon. Over the centuries the word polos has entered the language of the gnomonists of some countries to designate dials in which the direction of the style is parallel to the axis of rotation of the earth or again to designate the style itself when it is oriented in this fashion rather than along the vertical as is the case of the gnomon. There is a big difference here. Indeed, as we shall see, because of the sun's declination, none of the ancient gnomons discussed so far could give constant results throughout the seasons of the year. The length of the shadow at a given hour of one day does not correspond to that at the same hour the next day. There will be little enough difference between them at the solstices, but it will be considerable during the equinoxes; between a summer day and a winter day there is no possible comparison. On the polos dials, however, with the style parallel to the axis of the world, the reading of the hours is done with the same precision throughout the seasons. So we may assume that what Herodotus calls a polos is a dial which could have existed in Egypt in his time but about which no information has survived.
We must remember in connection with Herodotus' attribution of sundials to the Babylonians that he was disinclined to check on all the items of information supplied to him during the course of his travels. Taking account of the high level of Greek culture in the days of Herodotus and of the immense contribution of Greek thought in the domain of mathematics, we may posit that, in spite of the rarity of the hints in the written documents, the gnomon had been known to the Greeks for some time. In any event, in 560 BS, and therefore during the lifetime of Herodotus, Anaximander of Miletus installed a sundial in Lacedacmonia, the nature of which is not known to us. We can assume that, like the Chinese, the Greeks were using the gnomon as an instrument of observation around 600 BC.
We know too that in Herodotus' lifetime small portable dials of a peculiar shape were used in Egypt: the shadow of one edge fell on a horizontal plane divided into hours or on the steps of a small stairway, or at times on both of them at the same time. In this last instance, their shape suggests certain forms of Egyptian architec-ture or even, on account of their steps, the ziggurates of the old cities of Mesopotamia (figure 5). (We shall revert shortly to the strong probability of a Chaldean origin for these objects.) A later sample of this type of dial, from the fourth century BC, exhibits a definite improvement over the preceding type. The shadow fell on an inclined plane, on which lines scaled in hours had been drawn along the line of the steepest slope in such a way that the scale on each line corresponded to a given month of the year. Figure 6 shows a schematized representation of this dial, the first one in the history of gnomonics to take account of solar declination (the changing height of the sun at midday over the year). These later Egyptian dials imply, as does the earlier one in figure 2, that the shadow edge had been oriented first toward the sun.
It should be stressed that one thousand years had elapsed between the dial shown in figure 2 and those of figures 5 and 6, and that during that time sundials had obviously been in constant use. But we know absolutely nothing about them because of the scarcity of gnomonic finds in Egypt.
The presence of stair steps in the dial of figure 5 may serve to clarify some puzzling statements in the Bible about a sundial belonging to a certain king Ahaz, who reigned in Judea from 740 to 728, two centuries before the known appearance of the step dial in Egypt:
And Isaiah said "This is the sign to you from the Lord, that the Lord will do the thing that he has promised: shall the shadow go forward ten steps, or go back ten steps?
And Hezekiah answered, "It is an easy thing for the shadow to lengthen ten steps: rather let the shadow go back ten steps."
And Isaiah the prophet cried to the Lord: and he brought the shadow back ten steps, by which the sun had declined on the dial of Ahaz. (Kings 20: 9-11)
Elsewhere, we read (Isa. 38:8):
"... Behold, I will make the shadow cast by the declining sun on the dial of Ahaz turn back ten steps." So the sun turned back on the dial the ten steps by which it had declined.
In the book of Sirach or Ecclesiasticus (in the Apocrypha) we find another allusion (Ecclus. 48:24) to this famous dial of Ahaz:
In his days the sun went backward, and he lengthened the king's life.
The one thing we learn with certainty from these quotations is that the dial of Ahaz was provided with steps. But a close reading of the Book of Kings allows us to draw some additional inferences. Indeed, at a time when Ahaz was at war against both the Ara-means and the Israelites, he thought it would be proper to call to his help Tiglath-pileser, the then all-powerful king of Assyria. It happened that the latter, also engaged in a war campaign, had occupied the city of Damascus for almost ten years. The two kings agreed to meet in this city and, when Ahaz arrived, he was brought to an altar which interested him to such a point that, according to II Kings 16:10, 11:
When King Ahaz went to Damascus to meet Tiglath-pileser king of Assyria, he saw the altar that was at Damascus. And King Ahaz sent to Uriah the priest a model of the altar, and its pattern, exact in all its details.
And Uriah the priest built the altar in accordance with all that King Ahaz had sent from Damascus, so Uriah the priest made it before King Ahaz arrived from Damascus.
There are two possibilities. Either this extraordinary Damascus altar was already an ancient marvel – let us say, from before Ahaz's war, at least – which was certainly known to the great men of the surrounding countries, and therefore to Ahaz and his priests, because even at that time, the distance between Damascus and Jerusalem was far from prohibitive. Or this altar was a novelty built by the Assyrians after their arrival in the country in honour of their own gods. In the latter instance we would like to believe, taking special account of the enthusiasm of King Ahaz, that it was the step sundial he had built in Jerusalem his capital, and that this construction was of Chaldean origin since the Chaldeans, the then masters of gnomonics, were the vassals of Tiglath-pileser. Isaiah's hostility towards the new altar and the accusations which the Bible throws at Ahaz tend to prove the foreign and heretical origin of the whole installation. For if it were Chaldean, we would be able to trace, with some certainty, the step-type Egyptian sundial from the shores of the Nile back to Chaldea.
(Continues...)
Excerpted from SUNDIALS by René R. J. Rohr, Gabriel Godin. Copyright © 1965 Gauthier-Villars. Excerpted by permission of Dover Publications, Inc..
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