Aperture

“ If it has happened, as I surmise, that the aperture has been shut which communicated between the pit beneath us and the one above—if this has taken place, then we have a tank full of water over our heads. If we, in our search through the bowels of the earth, come upon this aperture, and accidentally break the smallest hole, not the size of a pin's point, the water in the basin over our heads will [Pg 414] burst through and annihilate us; if we hear it roaring we are already lost. ”

“ The opening in the centre, which appears like a black spot when the eye is examined, is not really an object, but simply an aperture, capable of changing its size according to the quantity of light striking the eye. ”

“ But if the observer meditates a critical analysis of the detail, either of a single spot, of a group of spots, or of a small area91 of the luminous surface, then a fair amount of aperture should be used, because greater aperture means greater separating power, and the latter will be useful in resolving the network of fibrous materials of which apparently the whole surface is composed. ”

“ When the breadth of the aperture is only a small multiple of a wave-length, then there will be some points outside the direct beam at which the disturbances from different points of the aperture will not completely destroy one another, and others at which they will destroy one another ”

“ Within this aperture, on the right hand, is a hole two feet diameter, perforated quite through the rock sixteen feet, and running from north to south. In the abovementioned aperture a man might lie concealed, and predict future events to those that came to consult the oracle, and be heard distinctly on the north side of the rock, where the hole is not visible. This might make the credulous Britons think the predictions proceeded solely from the rock-deity. The voice on the outside was distinctly conveyed to the person in the aperture, as was several times tried.'—Arch. ”

“ The peculiar character of the species, and in which it differs from all others, is in the outer margin of the lip; which is thin, rather spread out, and slightly reflected; the form of the shell resembles A. fasciata, but the spire, instead of being pointed, is obtuse; the umbilicus, likewise, is smaller and more concealed. From the absence of a groove round the aperture, I conclude the operculum is horny.
The size varies; perfect shells are in my possession much smaller than the figure, and I have seen others much larger, and with the aperture more chesnut than purple. ”

“ In such species as have a shelly operculum, the margin of the aperture is thickened all round, and has a parallel internal groove for its reception: the probable use of this groove I have detailed elsewhere. On the other hand, in those species which are known to have horny opercula, this margin and groove do not exist; and that part of the shell which is between the top of the aperture and the umbilicus, is thin and unprotected. This latter formation is by far the most frequent, and leads to the conclusion that the majority of these shells have their opercula horny. ”

“ In the case of the telescope we have to deal with a linear measure of aperture and an angular limit of resolution, whereas in the case of the microscope the limit of resolution is linear, and it is expressed in terms of angular aperture. ”

“ Eyes large, lustrous, beautiful, soulful; above them, no longer separated by rugged brow ridges, is the top of the head, a glistening, hairless dome, terete and beautiful; no craggy nose rises to disturb by its unmeaning shadows the symmetry of that calm face, no vestigial ears project; the mouth is a small, perfectly round aperture, toothless and gumless, jawless, unanimal, no futile emotions disturbing its roundness as it lies, like the harvest moon or the evening star, in the wide firmament of face. ”

“ V. A top supported above its centre of gravity, or a body which would be in stable equilibrium if not spinning, precesses in the opposite direction to that of its spinning.
VI. The last two statements come to this:—When the forces acting on a spinning body tend to make the angle of precession greater, the precession is in the same direction as the spinning, and vice versâ.
Having by observation obtained a rule, every natural philosopher tries to make his rule a rational one; tries to explain it. I hope you know what we mean when we say that we explain a phenomenon ”

“ Their high aerial flight the Cranes suspend,
And to the earth in broken ranks descend.
When the dull fire emits no cheerful rays—
With lustre dimm'd the languid torches blaze,
And the light cobwebs float along the air ”

“ A man can shake it so that the movement shall be shown in a vessel of water nearly seventy feet below the summit, and higher up the vibration is like that of an earthquake. I have seen one of those wretched wooden spires with which we very shabbily finish some of our stone churches (thinking that the lidless blue eye of heaven cannot tell the counterfeit we try to pass on it,) swinging like a reed, in a wind, but one would hardly think of such a thing’s happening in a stone spire. ”

“ A swift wind sometimes gave the balloon a rotary motion, which made me deathly sick for a moment; but strong emotion conquered all my physical ailings.
5. My brain ached with the intensity of my rapture. Human sounds had fainted from my ear. I was in the abyss of heaven, and alone with my God. I could tell my direction by the sun on my left; and, as his rays played on the aerostat, it seemed only a bright bubble, wavering in the sky, and I, a suspended mote, hung by chance to its train. ”

“ The velocity and various shiftings of the sun-beam, reflected from a piece of crystal or polished steel in the hand of a boy, give a much stronger idea of the violent agitation and sudden shiftings of thought than the image of the trembling light of the sun or moon reflected from a vessel of water. ”

“ When calms or light, variable airs occur, the number of hours of each is counted, and the sum entered in its proper place. When a gale—that is, wind of a force of 8 and upward—happens, the number of hours it blew from any of the eight principal points of the compass (supposing it to have varied in direction) , together with the force during each period, are duly tabulated. ”

“ We can picture such a mass, in imagination, tumbling end over end in its orbit so as to present at one moment the broad sides of both bells, together with their connecting neck, toward the sun, and, at the same time, toward the observer on the earth, and, at another moment, only the end of one of the bells, the other bell and the neck being concealed in shadow. ”

“ To seek to press a falling body by means of another placed upon it, is as senseless as trying to prod a man with a lance when the man is speeding away from one with the same velocity as the lance. Even this little excursion into physics can explain much to us. You know the peculiar sensation which one has in falling, as when one jumps from a high springboard into the water, and which is also experienced in some measure at the beginning of the descent of elevators and swings. ”

“ Now the small, glittering point of light seemed to recede, then to approach and expand, and then to wave and undulate all around him. Sometimes that bright, lightning-like ray would shiver and tremble, and then straighten out with metal-like rigidity, and insinuate itself into his very being like the invisible point of a spear. ”

“ Thus, I urged, when a man falls from a ladder because (as is commonly said) of the breaking of the rung on which his foot was resting, the real or dynamical cause of his fall is the force of gravity, or attraction of the earth, which pulls him to the ground when his foot is no longer supported; the loss of support being only the material condition or collocation, which allowed the force previously acting as pressure on the rung to produce the downward motion of the man who stood upon it. ”

“ Because, my dear Captain, we are moving through a vacuum, and because all bodies fall or move—the same thing—with equal velocity through a vacuum, no matter what may be their shape or their specific gravity. ”

“ That the descent is a mechanical effect of the whirlwind, which creating a vacuum, or high degree of rarefaction, extending between the clouds and the earth, the clouds descend in it by their gravity, or by the pressure of the surrounding clouds or air. That the convolutions of the descending mass, and the sensible whirlwind felt at the earth, as well as the appearance of the commencement, increase and decrease of the mass, all demonstrate the whirl of the air to be the mechanical cause. ”

“ A small periodical change of position in the stars and other heavenly bodies, due to the combined effect of the motion of light and the motion of the observer; called annual aberration, when the observer's motion is that of the earth in its orbit, and dairy or diurnal aberration, when of the earth on its axis ”

“ Suddenly there comes a hollow booming sound—a roar, mellowed and subdued by distance, with a peculiar beat upon the ear, as if a wave struck the nerve and rebounded and struck again in an infinitesimal fraction of time—such a sound as can only bellow from the mouth of cannon. ”

“ Now and again as they fed, the whole flock would rise momentarily into air and float up as though blown from the earth by some invisible breath, and then, as silently and simultaneously, sink to earth again. ”

“ Aberration is the apparent change in the direction of the luminous body due to the motion of the receiving body. The motion of the luminous body in the line of sight should alter the wave length of the emitted light due to molecular vibrations of given periodicity. ”

“ Otherwise I'm dying by inches. Why, man, you don't know what it was like. I used to get the most grand feelings—like a great rush of force, or light—a great rush—right here, as I've said, at the solar plexus. ”

“ The explanation of this phenomenon appears to me to be as follows: a wing, or any surface whatever, which moves against the air, meets, at the beginning of its motion, a considerable resistance, on account of the inertia of the air, which resists every displacement; but, little by little, the air yields, and the velocity of its motion gradually increases, until it may equal that of the moving surface which displaces it; this phase of motion having been reached, the resistance diminishes. ”

“ In a falling body we observe not only the deflection of terrestrial motion, but the falling body itself is composed of molecules and atoms which are in motion, and the earth also is composed of molecules and atoms in motion, and these paths are also deflected by the falling of the body. ”

“ In the first place, I shall take into consideration the general effects of attraction, or force; in which expression by the word force I mean pressure producing an effect on the motion of bodies that are free. Suppose we drop a stone from our hand, or from a high building, everybody knows that it begins to fall with a very small velocity, and that it gains velocity as it falls. ”

“ If I drop a stone from my hand, it falls to the ground. That which produces motion is a force: hence the stone must have been acted upon by a force which drew it to the ground. On every part of the earth’s surface experience shows that a body tends to fall. This fact proves that there is an attractive force in the earth tending to draw all bodies towards it.
Fig. ”

“ Now, motion under resistance takes a spiral direction, as may be seen by the motion of a body rising or falling through water. A bubble rising rapidly in water describes a spiral closely resembling a corkscrew, and a body of moderate specific gravity dropped into water may be seen to fall in a curved direction, the spiral tendency of which may be distinctly observed. ”

“ So great may be the strain exerted in the air, or whatever separates the two conducting bodies, that it may break down, and we observe sparks or bundles of light or streamers, as they are called. These streamers form abundantly when the force through the air is rapidly varying. ”

“ It is known that bodies in motion always describe some line or other in the air, as the whirling round of a fire-brand apparently makes a circle, the water-fall part of a curve, the arrow and bullet, by the swiftness of their motions, nearly a straight line; waving lines are formed by the pleasing movement of a ship on the waves. ”

“ To the central gloom of the midmost sky,
In our mazeful gyres we fly.
And our flight is a choral chant of flame,
That ceaseless fares to the outer void,
With the undersong of the peopled spheres,
The voices of comet and asteroid,
And the wail of the spheres destroyed. ”

“ We receive the impression of the falling of a large mass of water, descending always from the same height and with the same difficulty. The scattering of the drops of water, the formation of froth, the sound of the fall by the roaring and by the froth, are constantly produced by the same causes, and, consequently, are always the same. ”

“ And, shortly, out I went, high up in the air,—higher—higher,—until I thought that I [Pg 86] should never come down again. But, after a time, I felt that I was descending; and the fear came upon me that I might tumble back once more into the axis of the earth. If I had reflected a moment, I might have perceived that this would be impossible; for, as soon as I had sunk from my elevation down to a point not more than a hundred feet from the end of the pole, I met the swift current of air rushing out, and was once more hoisted up in the clouds. ”

“ If, on the path of a body falling vertically from rest, one lays off a portion which is traversed in any time you please and whose upper terminus coincides with the point where the motion begins, and if this fall is followed by a motion deflected along any inclined plane, then the space traversed along the inclined plane, during a time-interval equal to that occupied in the previous vertical fall, will be greater than twice, and less than three times, the length of the vertical fall. ”

“ As they sped on, lurching, jumping, piercing a broken wall of wave and spray like a torpedo, shooting an almost sheer fall, she came to rely on a sense of intuition rather than memory, for night had transformed the waters. ”