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Pagina 24 - Seriously, if we wish rural walks to do our children any good, we must give them a love for rural sights, an object in every walk ; we must teach them — and we can teach them — to find wonder in every insect, sublimity in every hedgerow, the records of past worlds in every pebble, and boundless fertility upon the barren shore; and so, by teaching them to make full use of that limited sphere in which they now are, make them faithful in a few things, that they may be fit hereafter to be rulers...
Pagina 539 - And another, which makes a straight many-chambered " test," that resembles in form the chambered shell of an Orthoccratite — the conical mouth of each chamber projecting into the cavity of the next, — while forming the walls of its chambers of ordinary sand-grains rather loosely held together, shapes the conical mouths of the successive chambers by firmly cementing together grains of ferruginous quartz, which it must have picked out from the general mass.
Pagina 635 - Y. ON THE MODE OF FORMATION OF SHELLS OF ANIMALS, OF BONE, AND OF SEVERAL OTHER STRUCTURES, by a Process of Molecular Coalescence, Demonstrable in certain Artificially-formed Products.
Pagina 465 - Supposing it to rest upon its convex surface, it consists of a lower plate, shaped like a deep saucer or watch-glass; of an upper plate, which is sometimes flat, sometimes more or less watch-glass-shaped; of the oval, thick-walled, flattened corpuscle, which connects the centres of these two plates ; and of an intermediate substance, which is closely connected with the under surface of the upper plate, or more or less...
Pagina 539 - Suppose a Human mason to be put down by the side of a pile of stones of various shapes and sizes, and to be told to build a dome of these, smooth on both surfaces, without using more than the least possible quantity of a very tenacious but very costly cement in holding the stones together. If he accomplished this well, he would receive credit for great intelligence and skill. — Yet this is exactly what these little "jelly-specks...
Pagina 385 - Fungus spreads by the extension of its own minute stems and branches ; and also by the production of minute germs, which are taken up by the circulating blood, and carried to distant parts of the body. The disease invariably occasions the death of the Silk-worm ; but it seldom shows itself externally until afterwards, when it rapidly shoots forth from beneath the skin.
Pagina 539 - Suppose a human mason to be put down by the side of a pile of stones of various shapes and sizes, and to be told to build a dome of these, smooth on both surfaces, without using more than the least possible quantity of a very tenacious, but very costly, cement, in holding the stones together. If he accomplished this 42 well, he would receive credit for great intelligence and skill. Yet this is exactly what these little 'jelly specks' do on a most minute scale; the 'tests' they construct, when highly...
Pagina 180 - ... of the fine motion, and move it briskly backwards and forwards in both directions from the first position. Observe the expansion of the dark outline of the object, both when within and when without the focus. If the greater expansion, or coma, is when the object is without the focus, or farthest from the Objective, the lenses must be placed farther asunder, or towards the mark
Pagina 805 - The result of this gentleman's researches * proves that granites have solidified at a heat far below the fusing points of their constituent minerals, and at such a pressure as to enable it to entangle and retain a small amount (£ to •£ per cent.) of aqueous vapour, which naturally must have been present during its liquefaction.
Pagina 216 - ... focal .length, as estimated by that of single lenses of equivalent magnifying power, a • temptation to underrate them being afforded by the consideration that if an objective of a certain focus will show a test object as well as another of higher focus, the former is to be preferred. Thus it happens that what are sold as £ inch objectives are often more nearly...