Percival Lowell

“ World-life has its earmarks of time as human life has, and betrays them quite as patently. Lack of atmosphere, colorlessness, changeless attitude toward the Sun, are the signs of old age in a planet. Mercury shows all these tokens of senility. Mars presents a very different picture. ”

“ If the affected body be distant compared with its size, the first term is enough, and we see that then the tide-raising force is directly as the radius of the second body, and inversely as the cube of its distance from the first, while also directly as the latter's mass.
But the work done by a force is the product of the force into the space through which it acts,—as, for instance, the lifting a weight a certain distance,—and in a given time the space is itself proportional to the force, whence the work in that time is as the square of the force. ”

“ The moment of rotation of a body of Mercury's mass is so great that it would take more than the Sun's might to suddenly alter it. The planet turns upon its axis, therefore, with a uniform spin. But its angular speed in its orbit is not uniform. Since the radius vector sweeps out equal areas in equal times, the angular velocity near perihelion exceeds that near aphelion. The revolution gains on the rotation here, and at the end of a certain time reaches its maximum ; after which the rotation gains on the revolution, and the deficiency is made up again at aphelion. ”

“ We think celestial mechanics abstruse enough as they are, but ours are child's play to the complications which two suns, to say naught of three or four, would introduce into any system over which they jointly held sway. It is problems of this nature which Professor Darwin and other modern analysts are trying to unravel. Difficult as the conceptions are, it is a question whether life itself would not be quite as difficult, under such conditions. ”

“ Take our nearest stellar neighbour, α Centauri, for instance, and consider what a planet circling round either or both of its suns would be called upon to undergo. Certainly our orderly succession of phenomena would be seriously disturbed to the consequent inconsequency of development upon its surface. Day and night would become meaningless terms, and organisms would have to put up with variations which make imagination stare.
For fashioning worlds like the terrestrial, a single-star system is, in general, a prerequisite. ”

“ In the disks of both we look only upon atmosphere and cloud. Lack of solidity, speed of self-movement, cloudy condition, are all so many signs of—youth. In relative—if not in absolute—age, both planets are still very young.
Semi-suns in several senses, the two planets are three-quarters way in their journey from nebula to world. In their traits both more closely resemble the Sun than the Earth. Indeed, with the trifling exception of not shining, the disk of Jupiter or of Saturn bears a very remarkable analogy to the solar. ”

“ Unlike the Moon, however, the illumination will not sweep over an invariable face, but lighting and lighted will rotate together ; for in the case of the Moon, we are the attracting, but not the illuminating, body ; in the case of a planet, the Sun is both. ”

“ Suppose, for simplicity, a body revolving round its primary in a circle and made visible by the light received from it. Furthermore, suppose the revolving body to have markings upon it, and to rotate once upon its axis as it makes one revolution round its sun. Clearly it will always present the same face to the central attracting and illuminating body, and therefore the markings will maintain an invariable position with regard to the illuminated face. To an outsider, the planet, if inferior, will present the phases of the Moon. ”

“ Then the inner parts of the mass that went to form the planet would be traveling fastest, and their momentum would prevail over that of the outer particles and give a retrograde rotation to the whole. Suppose, however, that the density increased toward the inner side of the mass. Then the centre of inertia would be so far shifted toward the inner edge, say to N, that the sum of the moments about it of the particles from without would, owing to their distance from it, surpass that of those within and a direct rotation result. ”

“ The points where the system in the light areas strike the dark are the points from which the canals in the dark regions set out. The two are thus but parts of one world-wide whole. Whatever purpose the one subserves is thus taken up and extended by the other. Nor does the communication come to an end in the dark regions. From the southern portions of these, in the southern hemisphere, other canals run straight into the polar cap; in the northern hemisphere, similarly, canals penetrate to the most northern limit of the snow. ”

“ The flash, the report, and the fused exterior of the mass found are due to the meteor's striking against our air. The bodies enter the upper atmosphere at speeds of from ten to forty miles a second, and such speeds are equivalent to immersing them in a blow-pipe flame of a temperature of many thousands of degrees. For the temperature of a gas is as the mean velocity-square of its molecules, and the rush of the meteor produces the same effect as if the molecules of the air were moving and the air therefore very hot. ”

“ As a detail of this, life on Mars must take on a very different guise from what it wears on Earth. It is certain that there can be no men there; that is as certain as anything well can be. But this does not preclude a local intelligence equal to, and perhaps easily superior to, our own. We seem to have evidence that something of the sort does exist there at the present moment, and has made imprint there of its existence far exceeding anything we have yet left upon mother Earth. ”

“ Consummation of tidal effect marks the last stage in the planetary career. So soon as identity of rotation and revolution is effected, the planet is placed in a changeless, or largely changeless, state, which, so far as we can conceive, means as a world its death. ”

“ Our own Solar System has one characteristic,Solar System a single-star one. a general family trait, which distinguishes it from many that lie round about it in space ; for we may not doubt that the stars are centres to systems of their own. We have not only analogy to guide us to this deduction, but we already have glints of evidence of the fact. Our system differs, how ever, from many of its neighbours in being a single-sun system. ”

“ If the effect of the Earth's rotation was merely to carry forward the crest of the tide through friction, it is the deep-water tides,—those in water over 123⁄4 miles deep, not the shallow, that would be nearest under the Moon.
Disturbing force. Consider a body revolving freely around another in a circle, and disturbed in this motion by a third. This is the case with any particle of the ocean when we neglect pressure and friction. Connect the three bodies by lines, and, keeping their directions, increase their lengths inversely
as their squares, and join the ends. ”

“ We have reached them without reference to the canals considered in themselves, and we should continue to put faith in them were the canals, with all their strange characteristics, blotted from existence. Unbeholden, then, to the canals for this conclusion, we are the more impressed to find that the supposition that the "canals" are not the result of chance falls completely in line with our result.
Water is very scarce on the planet, and is absolutely essential to life. Vegetation exists there, and it is therefore highly probable that organic life is to be found there, too. ”

“ The cause of the dissimilarity springs from the planet's size. The less mass of Mars did not permit it initially to present so fertile a field for development. Mere size entirely alters physical possibilities. In the next place, its dwarfing caused it to age quicker than the Earth.
Schiaparelli's discoveryOur knowledge of the planets, and especially of Mars, has advanced greatly within the last quarter of a century. The first steps of this advance we owe, not to instruments, but to the genius of one man, the Italian astronomer Schiaparelli. ”

“ Invisibility would be caused both by the comet's distance from us and by its distance from the Sun, for the commotion set up in these bodies, as they near the Sun, is chiefly responsible for the display they make.
The family undoubtedly consists of many more comets with greater perihelion distance.
Jupiter is not the only planet that has a comet-family. All the large planets have the like. Saturn has a family of two, Uranus also of two, Neptune of six; and the spaces between these planets are clear of comet aphelia; the gaps prove the action. ”

“ At Effect of frictionF, in consequence of the tide-raising force, the particle is traveling less rapidly than the rest of the Earth. Friction, therefore, urges it on and increases its tangential velocity up to some point P’ , where its speed becomes equal to the mean speed of the earth. After this, its speed being greater than the Earth's, friction retards it, until it again becomes the mean at P. Then friction begins again to accelerate it. ”

“ They go directly from certain conspicuously probable points to certain others. If we were obliged to connect the planet by a system of intercommunication, it is precisely those points we should ourselves select. In addition to the departure points on the borders of the dark regions which are provided by nature are a host of others not apparently so originated. These are the round black dots, the oases. They are found at the intersections of the lines. How important they are in the planet's economy is to be inferred from the host of canals each of them receives. ”

“ Jupiter's maximum effect in shortening comet's major axis The maximum effect in retarding the comet's motion occurs when the comet approaches Jupiter in such a direction and with such a relative speed as to be turned back upon the planet's path, and to leave the planet in the direction of the planet's quit, with a relative speed equaling the planet's own. It is then left stock-still to fall into the Sun. ”

“ Imagination is as vital to any advance in science as learning and precision are essential for starting points. ”

“ Until recently, mathematical astronomy dealt almost entirely with solids,—entirely so outside the consideration of the Earth. But no solid is absolutely rigid, and the action of one body upon another must cause mutual deformation of figure and give rise to tides in the two masses. ”

“ Picture a comet, coming in to the Sun from space, to pass close to the planet in its journey, Within a certain distance of Jupiter, the planet's pull becomes so great that it is mechanically more exact to regard the comet as obeying Jupiter and perturbed by the Sun ”

“ In the midst of the equalizing process the Sun, Jupiter, and Saturn now seem to be.
Jupiter has cloud layers.Jupiter, however, has progressed beyond the Sun in that the outer layers of his substance have cooled down enough to condense into cloud, due, possibly, to the planet's smaller mass. On the surface of the Sun things are still kept largely uniform by the terrific heat, and the slower rotation lets us perceive no latitudinal layers. On the contrary, Jupiter's disk is striated with belts of various tone and tint, according almost exactly to the parallels ”

“ A total eclipse of the Sun is commonplace beside it. Of the four hundred up to now observed, the greater part move in orbits differing so little from the parabolic for the small fraction of their paths we are privileged to mark that to all intent they travel in parabolas. They lean, however, to the side of the ellipse. Most of them frankly do so, although so slightly that to determine their major axes to any degree of accuracy is not possible. ”

“ Another point connected with these meteorMeteor streams attendant upon planets . streams must be noticed. Each of them is associated with the orbit of some particular planet. The planet in some sense shares with the Sun a control over the stream. It cannot cause the stream to circle round itself, but it can, and does, cause it to pay periodic obeisance to its might. The stream's perihelion remains at the Sun, but its aphelion becomes its periplaneta. It sweeps about the planet at the one end of its path somewhat as it sweeps round the Sun at the other. ”

“ Now probably no bodies are perfectly inelastic, just as no bodies are perfectly elastic. In the case, therefore, of the bodies in nature, while the amount of motion is never altered, a part of the kinetic energy is lost by the shock. It is transformed into heat energy.
Moment of momentum constant.Now the moment of a velocity, and therefore of a momentum, clearly remains constant when unacted upon by any force, for its direction continues the same, and a perpendicular upon it from any point measures out the same area in the same time, as the perpendicular, too, is constant. ”

“ The action of the planet is to turn the relative motion of the comet through an angle, say AOE, OA representing the in-coming asymptote of the relative orbit, OE the out-going one. EP or V' will then represent the absolute motion in space of the comet after the encounter. Similarly, if the comet passed behind the planet and was turned through the angle AOI, PI would be the new absolute velocity of the comet on leaving the planet. ”

“ From being a statical, it becomes a kinematical one, and the outcome is utterly different from what we might expect. Instead of bringing the plane of the equator into the plane of the ecliptic, it swings the pole of the equator round the pole of the ecliptic in a direction at right angles to the pull, and opposite to the rotation, but without changing the inclination of the two planes permanently at all. If the axis be in such position that the pull is perpendicular to the rotation, no change of inclination, even temporarily, occurs. ”