Percival Lowell

“ For upon one whole hemisphere of Venus the sun never shines, never so much as peeps above the star-studded horizon. Night eternal reigns over half of her globe! The thought would appall the most intrepid of our arctic explorers, and prevent at least everybody from going to the pole ”

“ For consider the surface indraught along the bounding rim of constant sun-exposure. With the immense temperature gradient which exists between the day and the night side of Venus, the power of these winds must be enormous. Being essentially surface ones, they must sweep the face of the planet with irresistible force and, what is more, having once found a pathway of preference, must from the general unchangeableness of the conditions continue to follow it perpetually. For the only thing to alter their direction, the libration, is from the circularity of Venus's orbit negligibly small. ”

“ It is popularly imagined that our gaze is concentrated on Mars, to the exclusion of much else, and that we are particularly concerned with its habitability. That this is a popular fallacy I shall show you tonight. For we shall contemplate together another planet in the light that study of the past thirteen years at the Lowell Observatory casts upon it, and we shall see not only that such a study has indicated it not to be habitable, but that the question of habitability has not in the least affected our research. ”

“ Curious as it may seem, the result is not to pull the bulge down into the orbit plane, but to make it back bodily along the ecliptic. It is as if the earth resented the sun's attempt to right it and with almost human perversity went the other way. Indeed one may feel the obstinacy of the thing by appropriately pressing on a gyroscope, when instead of yielding it will promptly buck against you with a force suggestive of intent. The greater your shove the faster its opposing speed. ”

“ In consequence tides of the whole substance are set up in them if they rotate, and these tides act as a brake upon the rotation until they finally retard it to coincidence with the orbital revolution.
That Venus now turns the same face in perpetuity to the sun, lets us look down a long vista in her career, and gives us a very instant idea of a phase in a planet's history: that long slow change by which a day is lengthened to infinity. That Venus should have suffered such action is in keeping with theory, though it could not have been predicted in the absence of fact?. ”

“ The rotation time of Venus, the determination, that is, of the planet's day, is one of the fundamental astronomical acquisitions of recent years. It is not a question of academic accuracy merely, of a little more or a little less in actual duration, but one which carries in its train a completely new outlook on Venus and sheds a valuable sidelight upon the history of our whole planetary system. For upon it turns our whole knowledge of the planet's physical condition. ”

“ One of the most striking features of Venus's disk are the tongues of shading that make in from all parts of the lighted rim toward the center. They are the beginnings of those spoke-like markings the methodical oddity of which makes their actuality so difficult of belief. They seem a thought too peripherally positioned to be other than optically evolved. ”

“ Not only as a clock is it a possibility, but as we shall see it has been actually so used unconsciously by man in days gone by, and his readings of it recorded in lithographs still legible to-day.
To understand its working we must in thought get off the earth and see that body from without. We should then perceive our globe as a mammoth top spinning in the sky as it moves along in its orbit. ”

“ The spin gives us our days, and as the equator is tilted to the path the pull of the sun is all the time trying to bring the one to coincidence with the other. If the earth were perfectly round there would be nothing for the sun to grasp and the spin would remain unchanged both in amount and in direction. ”

“ The Great Pyramid was in fact a great observatory; the most superb one ever erected. The building is the most mammoth in the world, and it had for telescopes something whose size has not yet been exceeded. This something which did those old astronomers for instrument was the Grand Gallery. As its name implies this was a stone gallery of imposing proportions set on an incline of 26° 17' in the very heart of the structure and pointing south. It is approached by the
The Great Pyramid Observatory. ”

“ So extended to-day is the astronomic field that to do good work one must specialize his endeavor, restricting himself to one particular branch of it and incidentally refraining, we may add, from discussing that of which he has not expert knowledge. Now research on the planets constitutes one such division, making as it were, an entity in itself. For diverse as the planets are to-day, they are all the result of one particular evolutionary process and knowledge of each member throws light upon the development, past or present, of the others. ”

“ But the portrait has its grand features for all that; features which give us a new conception of what exists in the universe and lure our thought afield in space with all the greater insistence for being drawn not from fancy but from fact. ”

“ For elongation, although the time when the planet is easiest seen, is not that in which it is best examined spectrographically for rotation.
In the case of a body reflecting light, the shift varies from what it is if the body be emitting it, from twice as much in some positions to nothing at all in others. This is because the reflecting surface itself moves to or from the waves. Thus if a planet be on the side of the sun away from the earth, the rim of it which is approaching the earth advances to meet each new wave and so shortens it by just the amount
The Planet Venus. ”

“ As these bodies are out of the plane themselves their action pulls the earth out of her orbital plane, causing a change in the obliquity of the ecliptic. There is in consequence a slow alteration in the place of the pole of the ecliptic and this results in a movement of the equator other than what the sun and moon produce. It is known as the planetary precession. Chiefly by such round-about process do the planets make themselves precessionally felt. For all of them, even Jupiter, are relatively too small and too distant to have their direct pull upon the earth's equatorial ring of any account. ”

“ Their dove-tailing at times is indeed surprising, so diverse the character of the converging lines of research. Thus that the planet's albedo should have anything to say about the length of its day, should actually come forward in corroboration of the markings' own forthright showing, would hardly have been supposed. Or that the ashen light of the dark side should find interpretation in the same axial rotation through a long chain of concatenated circumstance was not to be anticipated. ”

“ For Venus falls exactly on debatable ground, on the line as it were. Tidal action depends, for the time necessary to produce a given result, on the square of the radius of the body acted on and as the sixth power of its distance from the exciting cause. In consequence for solar action the nearer planets would show its effect first. Now Mercury already turns the same face always to the sun; the earth, as we know, does not. ”

“ When we thus reason about them—and even in science reasoning is not so much to be despised as some mechanical souls would have us believe—we see that they lose their oddity, becoming the very pattern and prototype of what we should expect.
Logical deductions from well-established fact has led us to explanation of what had seemed inexplicable or untrue. Our several results check one another. For, in conclusion, we may note how full of significance it is that the outcomes of such various investigation should fit into one another to an articulated whole. ”

“ By placing the slit parallel to the ecliptic or, more properly, to the orbit of Venus, which is practically the same thing, it would find itself along what we have reason to suppose the equator of the planet and thus by its tilt give evidence of the rotation period capable of measurement. Even a considerable error in the position of the equator would make little difference in the rotational result. In order that there might be no question of illusion or personal bias, photographs instead of eye observations of the spectrum were made. ”

“ Relatively so close is she to both bodies that to show she does not need the abetting background of the night, but without waiting for the sun's withdrawal may nearly always be seen in the daytime in clear air if one knows where in the sky to look. Situate about seven tenths of our own distance from our common giver of light and heat, she gets about double the amount of solar radiation that falls to our lot, so that her surface is proportionately brilliantly illuminated. Being also relatively near us, she displays a correspondingly large disk. ”

“ Light is due to wave-motion of the ether, and ordinary light consists of a mixture of light of various wave-lengths. By means of a prism or grating these are refracted differently and so sifted into a colored ribbon or band, the longer waves lying at the red end of the spectrum, as the ribbon is called, the shorter at the violet. Now the spectroscope is such a prism or grating placed between the image and the observer, by means of which a series of colored images of the object are produced. ”

“ Not less of interest is the way in which our knowledge has been obtained; for it has been acquired by research along very different lines, and then by reasoning upon the results of that research to their necessary conclusions. ”

“ The earth, however, is not round, but spheroidal, bulging at the equator. There is thus a handle, two handles in fact, which may be used for turning it. Now suppose the earth in the position of its summer solstice when its axis is tilted away from the sun in a plane containing the sun and a perpendicular to its orbit. The attraction of the sun tends to rotate it in this plane. Meanwhile the earth is spinning round its own polar axis at right angles to that direction. ”

“ It was reasoned by Doppler in 1842 that if an object be coming toward the observer emitting light as it does so, each wave-length of its spectrum should be shortened in proportion to the relative speed of its approach as compared with the speed of light, because each new wave is given out nearer the observer than would otherwise be the case and its wave-length thus seemingly decreased. ”

“ It is so combined with the latter, however, that though quite extensive in itself, amounting to more than 4°, it can never change the tilt of the ecliptic to the equator by more than 1°, one third on either side, so that our seasons can never differ greatly from what we know them now. They can neither be materially accentuated nor proportionately reduced.
Though the obliquity of the ecliptic is oscillatory, the motion of the ecliptic pole keeps persistently, though unsteadily, on always in the same sense. Its wanderings trace out an elliptic spiral which never returns into itself. ”

“ Such a thorough change in outlook upon the universe is certainly no mean event and serves to point the importance of a subject in astronomy well worthy of engaging general attention, the more so that it is intimately associated with man. For this revolution in the sky is brought about by what is called the precession of the equinoxes. ”

“ It might seem as if the best time to examine the planet for rotation were when it is farthest from the sun and is best seen. This indeed was the time selected by Belopolsky, who examined Venus spectrographically between the time of the inception of the investigation at Flagstaff and its execution and thought he had detected a short rotation for it. ”

“ Now with the earth the pull of the sun is feeble compared with the great moment of momentum of the earth, and in consequence the motion of the earth's pole is most leisurely. The backing of the equinoxes to meet the sun is but 50′′.23 a year and the time it takes to complete the circuit of the zodiac 25,700 years. ”

“ The fact-gatherer has his uses, but they are not those of the highest class. It is not enough to have a thing on our plates, we must know that we have it there and interrogate it for meaning if we would extract from it the knowledge it is capable of yielding and so most truly add to the advance of our day. ”

“ In this manner we discover that 4,690 years ago, or in 2780 b. c., the pole passed within 3' of arc of the star α Draconis. Practically the star was the pole, and it was the last bright star the pole approached before reaching Polaris. In the time of Hipparchus, 140 b.c., the pole lay undistinguished in a waste region of the sky. A of the dragon is now a star between the second and third magnitudes, but there is evidence to show that in ancient times it was brighter. It must
Map of the Northern Part of the Ancient Pyramid Field in Egypt. ”

“ In the next place the base of the building is four-square, its sides being oriented to the compass points with surprising accuracy. Just as Christian churches face the east, that is Jerusalem, and Mohammedan ones Mecca, so the pyramids faced the north. Here then we have surmise of both religion and astronomy, to wit astrology, embodied in the mere outward aspect of these constructions. ”

“ They would seem to us to narrow and become at the same time less salient as they advanced. This is just what their spoke-like character shows. Thus the peculiar look of the Venusian markings proves to be in exact keeping with what the conditions demand, and by so doing bears testimony that those conditions actually exist.
Not less strange on its face and equally interesting for its disclosure is another phenomenon connected with the planet which also has been deemed incredible—the exceeding brightness of Venus's disk. ”