Beyond the Milky Way

Front matter

Astron. Dept.

Copyright, 1925, 1926, by CHARLES SCRIBNER'S SONS

Printed in the United States of America

The Oriental Ancestry of the Telescope

Temp era il principio del mattino E il sol montavan su con quelle stello Ch'eran con lui quando l'amor divino Mosse da prima quelle cose belle." >> —,

The first astronomer was primitive man, who ordered his life by the stars. The daily course of the sun and his cheering return after the cold and darkness of the night; the advance from winter to summer, as the arc of the sun's path rose toward the zenith from its lowest limit in the south; the changing phases of the moon and the terrifying darkness of eclipses; the serene majesty of the midnight sky, sparkling with stars and rotating in slow and stately measure about the celestial pole: these and the wandering planets, the sudden meteors, and the rare comets, little noticed by modern dwellers in the glare of cities but of compelling splendor in the transparent atmosphere of the ancient world, deeply impressed the mind and the imagination of prehistoric man. Even in the Stone Age observations of the sun and moon are suggested by certain circles and crescents in neolithic art, replacing the animal portraiture of paleolithic times.

Thus early began the study of astronomy, starting from conceptions which, though simple and familiar, imply inductive thought, and aided by the clarity and definiteness of ideas of space and figure,

time and number, motion and recurrence. Unlike the invisible electrons, whirling in their orbits within the atom, or the microscopic organisms so vital in biological research, the brilliant members of the celestial host pursued their course before every eye, and invited study by their oft-repeated revolutions. Great laws of nature were open to discovery by any observer, armed only with clear vision and persistence of purpose. Hence it was that astronomy became the pioneer of the sciences, leading the way, not only in Egypt and Babylonia, but in Greece and the Moslem world, in the revival of research against the forces of mediævalism, and in the beginnings of modern investigation in Italy, France, England, and the United States.

In Egypt, where civilization arose, three influences were dominant: the sun, supreme as the great god Ra; the stars, abode of the blessed; and the Nile, fructifier of the fields. The earliest peasants based their year on the annual inundation of the Nile, and the date of its beginning became a matter of practical concern. This happened to coincide very nearly with the heliacal rising of Sothis (Sirius), whose first appearance on the horizon in advance of the sun was thus taken to announce the new year. Systematic observations began so far back that the first fairly reliable date in history, given by Breasted as the beginning of the year 4241 B. C., was thus fixed by this star.

The ancient Egyptian, in all the phases of his life, was severely practical. Like the Roman, but in sharp contrast with the Greek, he had little intellectual curiosity and in general he cared nothing whatever for the problems of science. Breasted has recently found, in the only known medical papyrus which is not merely a mass of magical formulas, that the old Egyptian author occasionally exhibits some interest in the symptoms of cases designated by himself as incurable. and have also given "definite indications of real progress in

mathematical thinking among the Egyptians." But, if we may judge from existing knowledge, these are individual instances, contrary to the national habit, lone exceptions that prove the rule. The priests, always powerful and sometimes in complete control of the government, directed a large part of the activities of the Pharaoh and people toward their own aggrandizement, as we may see from the fact that almost the only surviving structures on the Nile are enormous temples and tombs, their walls covered with the grotesque images of the gods and the complex ritual of the underworld. Monumental art was cultivated under rigorous control, almost exclusively for theological and mortuary purposes. Under such circumstances we cannot expect to find that the Egyptians contributed greatly to the progress of astronomy as a science.

However, the needs of common life and the daily routine and annual festivals of the temples demanded a reliable calendar and the subdivision of time, which could be provided only by astronomical observations. The priests became astronomers, and at a surprisingly early date, as we have seen, the opening of the year was fixed by the heliacal rising of Sirius. Contrary to the practice of the Babylonians, whose calendar was based upon the phases of the moon, the Egyptians determined their year by the annual return of the sun to a fixed point in the heavens, and measured its duration as three hundred and sixty-five days. With such beginnings, much might have been expected of a truly progressive people. But, as in the history of Egyptian art, which never surpassed the high level attained in the earliest dynasties, we find but few signs of scientific advance four thousand years later, when the Egyptians passed on their slight intellectual possessions to the Greeks.

For observations of the stars, the summit of a temple, commanding a free horizon under the cloudless skies of Egypt, admirably served the purposes of the astronomer priests. The eye was all that was needed to fix the year by observations of heliacal risings, but instruments for the determination of shorter time divisions were invented at a very early period. Through a fortunate discovery, the Oriental Institute of the University of Chicago has recently come into the possession of one of the earliest known instruments for observing the stars, made (as the inscription states) by no less a person than the Pharaoh Tutenkhamon, "with his two hands."

After returning from Egypt in the spring of 1923 Professor and I spent a month at the Villa Palmieri, near Florence, as guests of Mr. . Following his work at the tomb of Tutenkhamon, which I had been fortunate enough to see, Breasted was then writing of his previous discovery on the upper Euphrates of a remarkable Roman mural decoration, since published in his "Oriental Forerunners of Byzantine Painting." Through the kindness of Doctor , director of the Royal Astrophysical Observatory, we were enabled to observe the sun, moon, Jupiter, and Saturn with two of Galileo's original telescopes, preserved in the Galileo Museum at Florence, and attached for this purpose to the equatorial telescope at Arcetri. In a future article I shall endeavor to describe this attempt to see the heavens with Galileo's eyes. After these observations with the earliest of telescopes, Breasted went to London, where he discovered at a shop of a well-known dealer in antiquities a far older astronomical instrument, the

oldest, in fact, then known to him. It is best described in his own words, taken from a letter written shortly after his return to the United States, while I was still in London:

"I have been very much vexed since I last saw you because at our last meeting I forgot to show you a new and unknown monument of Tutenkhamon which I purchased in London a few days before I sailed. I mention it to you especially because the object turns out to be an astronomical instrument. It is a rectangular strip of ebony wood a little over ten and one-half inches long (perhaps intended for half a cubit), one and one-sixteenth inches wide, thickness just one-half inch. Along each edge, extending entirely from end to end, is an inscription stating that the object was made with his own hands, by King Tutenkhamon as a restoration of a monument of his father (meaning his ancestor) Thutmose IV. You may remember that the tomb of Thutmose IV contains a remark in ink on the wall reporting that his tomb was restored, of course after robbery, by Harmhab, who was practically the successor of Tutenkhamon. This

new monument which I am reporting to you can hardly have come from anything else than a tomb in view of the fact that it has escaped destruction for over three thousand years. If so, then the tomb of Thutmose IV had already been robbed under Tutenkhamon's reign, and the latter, whose own tomb was so soon to suffer from tomb-robbers, was endeavoring before the close of his reign to repair their depredations in the tomb of his ancestor Thutmose IV. It is of interest also that the object restored was an astronomical instrument. At one end of the ebony strip is a rectangular mortise hole a little over half an inch long, about three-sixteenths inch wide, and a scant one-fourth inch deep. It is clear that this mortise hole contained a tenon holding in place a little block mounted on the end of

the ebony strip. To the block was attached a plummet, and a vertical line, cut in the edge of the ebony strip exactly opposite the middle of the mortise hole, marks the place where the plummet cord descended. You will find the same instrument somewhat restored in 'Ancient Times,' page 78, Figure 59, marked A. I enclose a little sketch of the ebony strip in which I have restored the little end block from which the plummet was suspended. I do hope when you come through Chicago on your way to California that you will stop in Chicago and see it. My only justification for forgetting to show it to you in London is that I had not, at that time, recognized what the instrument was. It was only after studying the line marking the place of the plummet cord that I recognized the character of the object, the loss of the little block at the end rendering it by no means easy to recognize the thing. Its interest lies in the fact that it is the oldest of its kind, far older than the one published by Borchardt, which I have used in 'Ancient Times.'"

I have since examined this instrument, of capital importance to the history of science, and through Breasted's kindness I am able to give two photographs of it, together with the cut from "Ancient Times" to which he refers. It was known to the Egyptians as the "Merkhet," or "measuring instrument," and is of a type probably used for the orientation of temples as early as 3000 B. C. A complete example described by Borchardt dates from the sixth century B. C., more than seven hundred years later than the reign of Tutenkhamon.

This consists of a sight-vane, made from the middle rib of a palm-leaf, and a plumb-line suspended from an ivory support. One of the hieroglyphic inscriptions on the instrument reads: "I know the path of the sun, moon (?), and stars, each to its place." A meridian line was fixed by an observer sighting north through the slot (held close to the eye) toward the plumb-line, which was held at arm's length and moved east or west until it coincided with a star near the celestial pole. For time determinations two observers, each equipped with a complete instrument, probably sat facing each other on a north and south line. The hours were then defined by the moment at which certain northern and southern stars were seen to cross the vertical cord, aligned on the head, right or left eye, right or left ear, or other feature of the opposite observer. On the 16th of the month Paophi, for example:

1st hour. The leg of the giant, over the heart.

2d hour. The star Petef, over the heart.

3d hour. The star Ary, over the left eye.

4th hour. The claw of the goose, over the left eye.

5th hour. The hinder part, over the heart.

6th hour. The star of thousands, over the left eye.

7th hour. The star of S'ar, over the left eye.

8th hour. The finger point of the constellation of S'ar (Orion), over the left eye.

9th hour. The star of S'ar, over the left elbow.

10th hour. The star that follows Sothis, over the left elbow.

11th hour. The finger point of both stars, over the right elbow.

12th hour. The stars of the water, over the heart.

In Ptolemaic times, as Breasted adds, a picture of this instrument (the part made by Tutenkhamon) was used among the hieroglyphics as a determinative of the word "hour." In earlier times this word always had * after it, showing that diurnal time measurement was a stellar matter, doubtless determined by stellar observations. The Greeks called the whole instrument a "horoscope."

It is interesting to speculate whether the sealed boxes in the tomb of Tutenkhamon, of which many still lie untouched in the inner room adjoining the sarcophagus chamber, will contain one of these instruments. The whole household equipment of the Pharaoh was apparently placed in the tomb, and possibly this may have included a stellar transit. From the inscription already cited it is evident that

Tutenkhamon felt that the tomb of Thutmose IV, after despoilment by robbers, must again be provided with a "Merkhet," doubtless to count the passing of the hours in the nether world. After this mark of filial piety, it is to be hoped that Tutenkhamon's similar needs were not forgotten, and that a complete instrument of this period may yet come to light.

Sun-clocks were also used by the early Egyptians, and one of these, dating from the first half of the fifteenth century B. C., is illustrated in Fig. 6. The shadow of the crosspiece, which was turned toward the east before noon and then toward the west, indicated the time on the arm BB. The interval between sunrise (longest shadow) and noon (no shadow)

was divided into six hours, thus giving ultimately the twelve-hour day to Europe. Several other types of early Egyptian astronomical clocks have been discovered. One found at Gezer in South Palestine, dating from the reign of Mernepthah (about 1200 B. C.), is perhaps the most interesting as the probable prototype of our sun-dial (Fig. 7). An ivory disk, hung in a vertical plane, carried a projecting bar (gnomon) which cast a shadow on the dial, thus marking the hours in the familiar way.

Water-clocks, later used by the Greeks as the

clepsydra, also originated in Egypt. One marked with vertical scales on its inner face, indicating by the falling level of the water the twelve hours of the night (probably between darkness and dawn) for each of the twelve months of the year, was found in fragments in the temple of Karnak (Fig. 8). It dates from the period of Amenhotep III (about 1400 B. C.), and is made of alabaster decorated in color with constellations and planets, the sun and moon gods, and the king with the gods of the twelve months. The water was drained out through a small pipe, and the form of the vessel was designed to give an equal fall of water in equal times, as a papyrus found in Oxyrhyncus attests. But neither in this form of outflow clock, nor in a better type in which the water dripped into the vessel from another source, was any degree of accuracy attained.

Much has been written of the Great Pyramid, and many efforts have been made to prove that it was designed to be an astronomical observatory. No competent Egyptologist, however, supports this view. It was carefully oriented, and an open shaft was directed toward the pole of the heavens. But, as Breasted has pointed out, this is easily explained in harmony with its obvious design as the tomb of the Pharaoh. The ancient mortuary texts, inscribed in the chambers of the pyramids, recite that "the King lives among the imperishables." This refers to the belief that he was transmuted into a star, preferably one of the "undying" or "steadfast" stars, so called because they are near the celestial pole and thus never set.

As for the orientation of temples and pyramids, this was an extremely simple process, sufficiently well accomplished by directing a line toward the rising sun and one toward the setting sun, and bisecting the angle between them. Or the "Merkhet," as already mentioned, may have been employed. Biot, in discussing this subject, expressed his belief that whatever its original purpose, the Great Pyramid subsequently served as an immense gnomon for the determination of the time of the equinoxes, the dates when its east and west faces were grazed by the rays of the rising or setting sun. When still intact, with their perfect masonry and smooth finish, these faces would have served well for this observation, which after a few years of repetition might have measured the solar year to three hundred and sixty-five and one-quarter days, a quantity differing from the true value by about three-quarters of a day in a century. Even in 1853, when the disappearance of the smooth casing stones had already given the Pyramid its present step-like contour, Mariette, following Biot's instructions, thus determined the time of the vernal equinox within about twenty-nine hours. At that period the inhabitants of the neighboring villages knew that the rays of the setting sun at the equinox grazed the faces of the Pyramid, and the Sheik of Koneisseh told Mariette that the extremity of the shadow, which was about three kilometres long a quarter of an hour before sunset, fell near a granite rock a little north of this village.

The early establishment of the Sothic year, the orientation of pyramids and temples, and the invention and long-continued use of simple instruments, which were ultimately incorporated among the hieroglyphic characters and are also depicted in larger scale on the walls of temples and tombs, bear out the tales of early Greek travellers regarding the origin of astronomical observation in Egypt. But the apparent inability of the Egyptians to advance beyond their promising beginnings, and their failure to attack any of the real problems of astronomy, compel us to look elsewhere for the true foundations of astronomical research. In spite of a great admixture of superstition and magic, we find evidence of marked progress when we pass from the valley of the Nile to the banks of the Euphrates.

Fortunately for our knowledge of ancient astronomy, the cuneiform tablets of the Babylonians and Assyrians, far less fragile than the papyri of the Egyptians, have survived to our day in great numbers. When the royal library at Nineveh was enlarged by Assurbanipal, King of Assyria from 668 to 626 B. C., the added tablets included many relating to the astrology of the ancient Babylonians and the still more ancient Sumerian invaders. One series, known as "The Day of Bel," was ascribed by the wise men of the time to the period of the great Sargon I, about 2800 B. C. Guided by these antique documents, the soothsayers of the last Assyrian Empire reported periodically on both celestial and terrestrial happenings and predicted future events. High in rank and hereditary in office, the chief as- trologer and many other functionaries whose names have come down to us frequently addressed the king from all parts of the empire. The tablets contain astronomical reports and astrological deductions based upon them. If the moon's horns were observed to be pointed, "the king will overcome whatever he goreth." The moon was also supposed to influence sheep and cattle, and lunar as well as solar halos were eagerly watched as a means for prediction, especially of rain. Omens were also based on the entrance of the planets into the signs of the zodiac, while eclipses, as sources of disturbance, called for supplications to the protecting gods.

Although the Assyrians and Babylonians were so famed for astrology and magic that the very name "Chaldean" became synonymous with sorcerer, it remains true that they contributed notably to the establishment of astronomy as a science. Passages in their astrological tablets indicate that the calculation of times and seasons was a prime duty, and there is some evidence that they possessed instruments for measuring time. The term abkallu sikla on one of the astrological tablets is translated "measure-governor" by Thompson, who believes it to represent some kind of clock. From the early appearance of the water-clock in Egypt, and the attribution of the clepsydra or some other form of time-measurer to the Chaldeans by Sextus Empiricus and Herodotus, there is little doubt of the correctness of this conclusion. Their tablets also mention a time unit, called kasbu, equal to two hours. A watch consisted of two kasbu, and three watches completed the night. The Assyrian year contained twelve lunar months, usually of thirty days each, with an intercalary month added from time to time. Even during the earliest period the tablets contain

many lists of stars, observations of the moon, eclipses, planets, comets, altitudes of the sun and moon, etc. After the seventh century B. C. the interests of astronomy were more clearly recognized and no indications of the art of the diviner are found in a large body of tablets of this period.

These tablets are of two classes, one containing observations, the other computations. The obser- vational tablets include the positions of the sun, moon, and especially the planets, the latter given with reference to neighboring stars. At first a star was designated as indicating the place of a planet in its vicinity. But during the last four centuries B. C. angular measurements of position were made, though nothing is yet known as to the nature of the instruments employed. A high degree of precision was attained in the determination of the period of revolution of the planets, and eclipses of the sun and moon were successfully predicted.

One of the oldest computational tablets yet discovered is in reality a page from an astronomical ephemeris computed for the year 425 B. C., the fortieth year of Artaxerxes I. The left-hand column, both on the obverse and reverse sides, contains for each month the length of the month, the date of full moon, and the date of the moon's last visibility. The right-hand column predicts the dates of the heliacal rising and setting of planets and stars. On the reverse two additional predictions are included, as follows:

On the first Mercury rises.

On the third the Equinox.

Night of the 15th, 40 minutes after sunset an eclipse of the moon begins.

On the 28th occurs an eclipse of the sun.

Kugler, who translated the tablet, calculated that these eclipses actually took place on October 9 and 23, in 425 B. C. The eclipse of the moon was vis-

ible in Babylon, but that of the sun could be seen only at some distance from the city.

These predictions of the Babylonian astronomers were undoubtedly based on their discovery of the Saros, the eclipse cycle of eighteen years and eleven days, or two hundred and twenty-three lunations, after which the same succession of eclipses recurs, though not at the same places. It was from Babylonian sources that travellers like Herodotus derived the elements of the astronomy which the Greeks rapidly developed into an exact science. In fact, a Babylonian quoted by as Kidénas and by Pliny as Cidenas has been identified as the author of a cuneiform tablet of moon data signed by the astronomer . It cannot be said, in spite of the value of their observations, that the Babylonians made any original contributions to the instruments of the astronomer. The gnomon and the sun-dial, attributed to them by Herodotus, were used centuries earlier by the Egyptians, and the water-clock, as we have seen, was also of Egyptian origin. Nevertheless, the long practice of astronomy by the Babylonians, the care and accuracy of their observations, and the imposing towers used as their observatories, profoundly influenced the Greeks. The ruins of the temple of Bel, from whose summit the astronomer priests observed the heavens for centuries, must have deeply impressed the scholars who accompanied Alexander the Great on his campaign in India and the Near East. As Draper remarks, the stimulus of the discoveries made by this expedition, among the widest variety of geological formations and paleontological remains and the strange and varied fauna and flora between the cataracts of the Nile and the banks of the Indus, aided in preparing the way for

the remarkable researches of the Greeks, the true founders of modern science.

Homer and other ancient poets had conceived the earth to be a plane surface, encircled by the ocean, where the heavenly bodies rise and set and the burning sun hisses as he plunges beneath the waves. The Ethiopians, living near the margin of the earth, were therefore supposed to be scorched by the sun's close approach. This fabulous age was soon succeeded by the most striking developments, due to the extraordinary powers of the early Greek mathematicians and astronomers, who derived stimulating suggestions, primitive instruments, and important observational data from Egypt and Babylonia. (about 600 B. C.), who learned in Egypt the empirical geometry of the priests, rapidly developed abstract geometry, and mathematics was raised to a science by Pythagoras, Apollonius, Euclid, and other members of the Alexandrian School. At the same time astronomy made equally striking advances.

The apparent annual motion of the sun among the stars is the basis of astronomy, and the knowledge of the sun's path gained by the Egyptians and Babylonians was brought to Greece at a very early period. The obliquity of the ecliptic, or inclination of the sun's path to the celestial equator, was measured by Meton in the year 430 B. C. Doubtless he employed a gnomon, the simplest of the astronomical instruments handed down by the Egyptians and Babylonians. It consists merely of a vertical pillar, whose shadow gives the direction and altitude of the sun. The lengths of the longest and shortest shadows, cast by the gnomon at noon at the time of the winter and summer solstices, afford the means of determining the obliquity of the ecliptic. An- other very early instrument is the hemispherical sun-dial, in which the position of the shadow of a point at the centre of a hollow hemisphere was read on the concave surface marked with circles. A huge

existing example of this is the "Jai Prakas" of the Hindu Maharajah Jai Singh (Fig. 12).

Practical and religious needs and the art of divination largely controlled the astronomy of the Egyptians and Chaldeans. The Greeks, on the contrary, show from their beginnings an entirely different attitude, sometimes weakened by mysticism, but in most cases identical with that of the modern in vestigator. Nearly four centuries before the Christian era developed a geocentric theory of the solar system and endeavored to test it by observation. (310–250 B. C.) held, in early anticipation of Copernicus, that the apparent motions of the sun, moon, and stars are due to the rotation of the earth on its axis and its revolution around the sun. Aristotle objected that in this case the stars should appear to shift in position when viewed from opposite ends of the earth's orbit. Aristarchus, in spite of the prevailing opinions of his time, replied that they were too far away to show any sensible change in direction. He was right, but the lack of instruments capable of detecting their excessively small parallax, or annual displacement, caused by the earth's motion, made possible the dominance of the geocentric doctrine set forth by Ptolemy in the Almagest, an astronomical classic that controlled human thought for fifteen centuries.

This truly remarkable book, which embodies the results of and other astronomers who preceded Ptolemy, reveals both the strength and the weakness of Greek science. Following Aristotle, , and others, Ptolemy clearly demonstrated the sphericity of the earth, which he fixed at the centre of the concave sphere of the heavens. He ridiculed those who believed in the earth's orbital motion and axial rotation, and proved to his own satisfaction that the sun, planets, and stars revolve about it. The changing distances of the sun and moon, shown by their variation in apparent diameter, had been attributed by Hipparchus to a displacement of the earth from the centre of the circles in which they were supposed to move. To account for the backward and forward motions of the planets, which actually result from the modification of their steady orbital motion by the revolution of the earth about the sun, Hipparchus invented the system of epicycles, in which each planet is supposed to rotate in a small circle about a centre which moves at uniform speed in a large circle around the earth. These artifices sufficed to represent the motions of the sun, moon, and planets as then roughly known, and through the support of the Church and the wide-spread use of the Almagest, the Ptolemaic theory held sway until the reasoning of (1473–1543), the improved observations of (1546–1610), the formulation of the laws of planetary motion by (1571–1630), and the discoveries of (1564–1642) finally led to its downfall.

The star catalogue in the Almagest remained until the time of Tycho Brahe the only widely available list of the positions and brightness of stars. The observations on which it is based were actually made by (about 130 B. C.), the greatest astronomer of antiquity. Fortunately, Ptolemy preserves for us a description of the instruments used by Hipparchus and other early Greek astronomers. In principle, most of these consist essentially of a graduated arc of a circle, ranging from a sextant to an entire circumference, supported in the plane in which the measure is to be made.

The simplest of these instruments, used for observing the altitude of the sun at the solstices, and thus for determining the obliquity of the ecliptic and the length of the year, probably goes back to the time of and , whose observations were made in the great Museum of Alexandria about 300 B. C. It consisted merely of a copper ring, graduated with degrees and subdivisions, and mounted vertically in the meridian. Within it a second ring rotated in the same plane. This carried two diametrically opposite pins, with pointers for reading the circle. The altitude of the sun at noon was measured by turning the inner ring until the shadow of the upper pin fell centrally on the lower one.