Layer

“ Suppose all below this line to be a thin layer of particles which, keeping compactly together, form a solid sheet of particles, every one of which touches the paper. This would be the solid earth to a being in the plane world.
Let the surface of the paper above this be covered by a layer of particles which move freely amongst each other, but which do not rise from the surface of the paper. These particles form the air of such a world.
On the surface of the earth draw a line standing upright. Let this line represent a man. ”

“ The solid part of the earth is therefore composed of (1) a thin layer of unconsolidated or earthy material, a few feet to a few hundred feet in thickness, covering (2) a layer or zone many thousands of feet, and probably many miles, thick, composed of solid rock comparable to that exposed at numerous points on the surface, and (3) a central mass, to which the preceding layers are but a shell, composed of hot, dense, and rigid rock, the real nature of which is not known by observation. ”

“ We conclude from all these evidences that there exists on the surface of solid bodies an extremely thin layer, the density of which diminishes the more nearly we approach the free surface. Let us assume, consequently, such a special constitution for the superficial layer of solids, and, by a new effort of our imagination, witness the unrelaxing work of our particles of air in the immediate vicinity of some solid body ”

“ As a forest becomes denser, its layers disappear from the upper downward, the ground layer always being the last to disappear because of its ability to grow in very diffuse light. A vertically zoned formation shows a complex series of reactions. The primary layer determines the amount of heat, light, water, wind, etc., for the subordinate layers in general. Each of these layers then further determines the amount for those below it, the ground layer being subject in some degree to the control of every layer above it. ”

“ By stripping off layer after layer we reach eventually a last layer which is all surface, inclosing nothing. We may, if we please, observe something analogous in men, among whom the most superficial have the least in them. In consequence of this principle, the atmosphere of the smaller body finds itself obliged to cover relatively more surface, which still further thins it out. ”

“ A layer represents the growth of a year. Where these are accessible, there is no difficulty in ascertaining the age of a tree, or the rate of its growth; and the rate thus ascertained may be applied to other trees of its kind whose diameter is known, although its woody layers he inaccessible. ”

“ The scales, which have been compared to the scales of a fish or to slates on a housetop, overlap each other, the free edges protruding more or less from the fibre, while the lower or covered edges are embedded and held in the inner layer of cells. ”

“ In many parts if you could dig straight downwards through the earth for thousands of feet, you would come to layer after layer of these stratified rocks, one kind below another, some layers thick, some layers thin, here a stratum of gravel, there a stratum of sandstone, here a stratum of coal, there a stratum of clay. ”

“ In placing one layer vertically over another there are three possible arrangements, of which only two concern us. In the arrangement for closest packing, B, say, a molecule of any one layer touches three molecules in each of the layers above and below, which with the six it touches in its own layer make twelve altogether. ”

“ The materials of the earth occupy more space when they are hot than when cold, and as the interior portion is still cooling, the outer layer or crust continues to shrink down upon it, forming folds or wrinkles, as in the case of the skin of an apple. ”

“ All surfaces are covered with a thin adhering layer of air, which it is difficult to remove, and which, although it may at first sight seem improbable, bears a relation to the outer surface of most bodies different from that maintained by the air a few lines away. ”

“ When beds of sand, clay, and marl, containing shells and vegetable matter, are found arranged in a similar manner in the interior of the earth, we ascribe to them a similar origin; and the more we examine their characters in minute detail, the more exact do we find the resemblance. Thus, for example, at various heights and depths in the earth, and often far from seas, lakes, and rivers, we meet with layers [p.4] of rounded pebbles composed of different rocks mingled together. ”

“ To obtain a general idea of the nature and method of our science before beginning its study in detail, we may visit some valley, such as that illustrated in the frontispiece, on whose sides are rocky ledges. Here the rocks lie in horizontal layers. Although only their edges are exposed, we may infer that these layers run into the upland on either side and underlie the entire district; they are part of the foundation of solid rock which everywhere is found beneath the loose materials of the surface. ”

“ Neither has sufficient attention been given to the influence of the state of the surface, or that of the thickness of the layers and their internal structure on the quantities of heat which freely pass through them. ”

“ You are, doubtless, all aware that the outer substance of the earth, which alone is accessible to direct observation, is not of a homogeneous character, but that it is made up of a number of layers or strata, the titles of the principal groups of which are placed upon the accompanying diagram.68 Each of these groups represents a number of beds of sand, of stone, of clay, of slate, and of various other materials. ”

“ Now we find that those portions of the earth immediately beneath our feet, extending for a mile or so into the surface of the earth, are variously made up of layers, strata, beds, formations, lying on one another, and conformable or unconformable, undisturbed or thrown into anticlinal or synclinal folds ”

“ There are formed successive layers relatively friable in texture, each of which, thickest at the most exposed parts, and being presently lost by weathering, leaves the contained mass in a shape more rounded than before ”

“ Whether the glad flames sport amid the long dry grass of last year, or the plough turn up a deep layer of the exhaustless soil, or flocks of prairie-chickens fly up from every little valley, images of life, joy, and plenty belong to the scene. The summer flowers are not more cheerful than the spring blaze, the spring blackness of richness, or the spring whirr and flutter. The sky is alive with the return of migratory birds, swinging back and forth, as if hesitating where to choose, where all is good. ”

“ Meanwhile differences in consistency appear in various strata, and a dense outer protective layer (peridium) , soft gelatinous layers, and so on are formed, the whole eventually attaining great complexity—e.g. ”

“ The complete working out of this arrangement with reference to light produces typical subordinate association, which finds its characteristic expression in the layering of forests and thickets. Layers tend to appear as soon as open woodland or thicket begins to pass into denser conditions, and up to a certain point, at which they disappear, they become the more numerous and the more marked, the denser the forest. ”

“ Follow with your eye any two adjacent lines, and you will see that where they are close to each other the surface has an abrupt change of level; where they are further apart the surface is nearly horizontal. Where the surface approaches the perpendicular, as on the sides, the dark line showing the separation of the strata is thin, because it has been cut through nearly at right angles. Where the surface is more horizontal the dark line is broader, because it has been cut through obliquely, the breadth varying steadily with the angle of inclination. ”

“ A natural extension of either of the methods already described will give us a series of surfaces in which every one is the surface, or every one the surface for a body of constant composition, the proportion of the components varying as we pass from one surface to another. But for a simultaneous view of the properties which are exhibited by compounds of two or three components without change of temperature or pressure, we may more advantageously make one or both of the quantities or constant in each surface. ”

“ Where are all our intermediate distances to come from?—how are we to express the aerial relations among the parts themselves, for instance, of foliage, whose most distant boughs are already almost black?—how are we to come up from this to the foreground, and when we have done so, how are we to express the distinction between its solid parts, already as dark as we can make them, and its vacant hollows, which nature has marked sharp and clear and black, among its lighted surfaces? ”

“ The outer circle, coat, or contour, of which you have heard others besides myself speak, is the surface crust of our globe, the great sphere of land and water on which man is at present an inhabitant. ”

“ That every visible figure will be represented by that part of the surface of the sphere, on which it might be projected, the eye being in the centre. And every such visible figure will bear the same ratio to the whole of visible space, as the part of the spherical surface which represents it, bears to the whole spherical surface. ”

“ Reflexion.—When rays of light fall upon a plane surface, as the flat surface of the mirror, a greater or less number of them are reflected, and this according to a definite law, by which the angle of incidence, or that formed by the incident ray with the perpendicular, is equal to the angle of reflexion, or that formed by the reflected ray with the same. ”

“ Fig. 56 shows the manner of holding the smooth plane in releasing the wedge, as well as when the cutting edge projects too much.
[35]
26. Planing First Surface True. —A true surface is one which is straight as to its length and width and which has its surface at the four corners in the same plane. Select for this first surface, which we shall call the face side, the better of the two broad surfaces. Knots, sap, wind, shakes, etc., should there be any, must be taken into account when passing judgment. Often the two sides are so nearly alike that there is little reason for choice. ”

“ Let’s see from what you would define a mirror—from a surface per se, in quantum est superficies, or from a substance that forms the surface, or from the substance upon which the surface rests, the raw material, modified by the attribute ‘surface,’ since it is clear that, surface being an accidental property of bodies, it cannot exist without substance. ”

“ Upon examining various portions of the earth's surface, they will be found to differ in character from each other; in one place perhaps sandy soil will be found, in another, hard rock, in a third, clay, in a fourth, chalk, and so on. ”

“ A surface is defined to be length and breadth without depth; a line to be length without breadth or depth; a point to be what has neither length, breadth, nor depth. 'Tis evident that all this is perfectly unintelligible upon any other supposition than that of the composition of extension by indivisible points or atoms. How else could any thing exist without length, without breadth, or without depth? ”

“ The outer surface of a pencil line represents the surface of the earth; the inner surface of the line represents the depth of man's explorations; the highest mountain would be represented by a comma resting on the line. ”

“ And the parts of the envelops of the rolling plane between these lines, although a continuation of the developable surfaces which have been described, and representing states of the body, of which some at least may be realized, are of minor interest, as they form no part of the surface of dissipated energy on the one hand, nor have the theoretical interest of the primitive surface on the other. ”

“ Again, if a body be considered as having superficies, and be understood to be so moved, that all the several parts of it describe several lines, then the way of every part of that body is called thickness or depth, and the space which is made is called solid, consisting of three dimensions, any two whereof are applied whole to every several part of the third. ”

“ Imagine a vast sheet of paper on which straight Lines, Triangles, Squares, Pentagons, Hexagons, and other figures, instead of remaining fixed in their places, move freely about, on or in the surface, but without the power of rising above or sinking below it, very much like shadows—only hard and with luminous edges—and you will then have a pretty correct notion of my country and countrymen. ”

“ The natural world may be conceived of as a system of concentric circles, and we now and then detect in nature slight dislocations, which apprize us that this surface on which we now stand is not fixed, but sliding. ”

“ We notice the distribution of light and shade; a morning or evening landscape, a shaded face or sphere, looks deeper, more solid, more plastic, than the landscape at high noon or the outline drawing. We notice the course of boundary lines and the visibility of surfaces ”

“ If at each point of the given surface we measure off along the normal one and the same distance at pleasure, then the locus of the points thus obtained is a surface cutting all the normals of the given surface at right an les, or, in other words, having the same normals as the given surface ”

“ So in successive strata the present surface of the world was built, and sometimes in throes of uplifting, some long-buried stratum was doubled upon itself, and having been thrust up through deposits lying above it, once more reached sunlight. ”

“ The surface of the globe, says Woodward, this external stratum on which men and animals walk, which serves as a magazine for the formation of vegetables and animals, is, for the greatest part, composed of vegetable or animal [196] matter, and is in continual motion and variation. ”

“ I represents the surface of the Earth divided into land and water. Were all land on our Earth put together in a circle, and the water placed round it, then the land would only fill the inner circle, the water occupying the surrounding ring, a space nearly four times as large as the circle. Fig. II, III, IV, V and VI represent the comparative surfaces of America, Europe, Asia, Africa and Australia. ”