Imatges de pÓgina

and distillation, arts totally unknown to the Greeks and Romans. What was the distinguishing character of this age? Mental darkness brooded over the fairest regions of the Christian world. The wrecks of knowledge lay buried in the convents, and the more active spirits exerted all their energy in violent sports or savage depredations. What was Rome at this period? The centre of the Christian commonwealth, and multitudes resorted from all parts to enjoy the refinements of Italy, which were reflected to the remotest corners of Europe. What was the distinguishing character of the twelfth to the fourteenth centuries? The pilgrimages over Europe, and the crusades undertaken against the Saracens. Were those expensive armaments for military exploits of any use to Europe? Yes; they may be regarded as the main cause of the renovation of the human intellect, and the origin of many of the subsequent improvements which advanced the progress of society in Europe. Were any improvements made in the most valuable arts during the middle ages? The curious process of converting cotton and linen rags into paper was invented about the beginning of the eleventh century. Who first constructed spectacles? Salvino degli Armati, about the year 1285. Was the attractive power of the magnet known to the Greeks? Yes; but they remained ignorant of its more wonderful properties. Who discovered the magnet's wonderful property of pointing towards the north? The Chinese, hence it got the name of load-stone or leading-stone. Where was the first compass in Europe made? At Amalphi, near Genoa, about the close of the thirteenth century. Were the eastern nations long acquainted with the deflagrating property of nitre or saltpetre? Yes; and this wonderful substance was first imported into Europe by the crusaders. Who made the important discovery of

its explosive force? Schwartz, a German monk, about the year 1382. But what nobler trophy distinguished the same period? The modern art of printing by means of combined moveable types was invented about the middle of the fifteenth century. What did the ingenuity and perseverance of Guttenburg and Schoeffer confer on the human race? They conferred by far the greatest benefit ever bestowed upon the human race, for in the short space of thirty years they carried this invaluable art to its highest perfection. Who contrived the art of engraving? Schoeffer likewise, and executed in 1491, for Arndes, burgomaster of Lubec, a series of figures of plants and animals on wooden blocks. What language was adopted as the medium of intercourse over Christendom? The Latin language. Whence may the day-spring of reason be dated? From the middle of the sixteenth century the tide of discovery has flowed in a rapid and majestic stream, philosophy and the arts reflecting mutual lights. Who began now to explore the wide fields of human knowledge? Copernicus partly restored the true system of the world; Purbach and Muller abbreviated the calculations of the astronomer, by their original improvements in trigonometry. What improvements did Ubaldi and Stevinus make? They extended the principles of mechanics and hydrostatics. What improvements did the fine genius of Galileo make? He detected and applied the laws of motion, and reinvented and constructed the telescope. What did the bold and exuberant imagination of Kepler accomplish? He drew aside the veil and disclosed to view those eternal laws which govern the revolution of the heavenly bodies. Who was distinguished as a calculator? Our great countryman Napier rendered himself immortal by the sublime discovery of logarithms. Who appeared the most distinguished philosopher in England in the

seventeenth century? Dr. Gilbert of Colchester, whose merit stands very high. His treatise on the magnet was a distinguished model of the application of philosophical analysis. Gilbert not only established terrestrial magnetism, but laid the foundation of electricity. Who reduced the principles of optics into a systematic form? Kepler. Who discovered the law of incidence and refraction? Snellius. Who unfolded the properties of light, and the brilliant phænomena of the rainbow, and applied algebra to geometry? It was Des Cartes. What country produced the thermometer and barometer? Italy, which Torricelli invented after the death of his master Galileo. Who discovered the construction of the air-pump? Otto Guericke in Germany, and employed it in the investigation of various important phanomena. Who first taught the way to investigate nature? Bacon. Who arose about this period to bear away the palm of triumph in science? Newton followed Bacon, and illustrated his precepts by the most sublime discoveries which one man has ever made. Newton's fine researches in optics, as they began, so after a long interruption they closed his scientific labours. What did Newton and Leibnitz separately discover about the same time? They discovered the method of fluxions, or the differential and integral calculus. When did electricity aspire to the rank of a science? In the year 1745 when the Leyden jar was invented. Was the combination of alternate metallic plates of the ingenious Volta, called the pile, deemed an improvement in the history of science? Yes; in the skilful hands of Davy, Berzelius, and Dr. Ritchie, the voltaic pile has displayed the most astonishing results.



What do you mean by a law of nature? A certain fixed and determinate rule, in obedience to which the same event always happens in the same circumstances. Thus it is a fixed rule, and therefore a law of nature, that every body, when left unsupported, will fall to the ground. What do you understand by the term body? A quantity of matter of any kind whatever, whether of wood, stone, glass, water, air, &c. What are the general properties of bodies? Extension, impenetrability, divisibility, porosity, gravity, and inertia. What is meant by the geometrical, and what by the physical form of bodies? By the geometrical form of a body we understand its dimensions in space, by its physical form we mean the peculiar properties by which it distinguishes itself from others of the same volume. What do you call the attraction of a liquid to the sides of a narrow tube which is immersed in that liquid? It is called capillary attraction. What is necessary in order that a liquid shall rise in a capillary tube? That the tube must be made of a substance which attracts the particles of the liquids stronger than they attract each other. What do you mean by the centre of gravity? That point of a body about which, if supported, the whole body would balance itself in every position. How many simple mechanical powers are there? Six: the lever, wheel and axle, pulley, inclined plane, wedge, and screw. What is a lever? An inflexible bar either of wood or metal, which turns on a joint or fulcrum, placed either at one end of the lever or somewhere between its two ends. How many kinds of levers are there? There are three kinds of levers. The first has the fulcrum between the

power and the weight. The second has the weight between the fulcrum and the power. The third has the power between the fulcrum and the weight. In the first kind of lever, what is the pressure upon the fulcrum equal to? The sum of the weight and power. In a lever of the second kind, a power of three acts at a distance of twelve; what weight can be balanced at a di3 x 12 36 = stance of four from the fulcrum? 4

= 9

weight. In a lever of the third kind, the weight is 60 and its distance 12, and the power acts at a distance of 9 from the fulcrum; therefore,

60 × 12

= 80, the

power required. Examples of levers of the first kind handspikes, crow-bars, scissors, pincers, snuffers, balances, pokers, steelyards, the hammer for drawing nails. Examples of levers of the second kind, oars, bellows, the helms of vessels, doors on hinges, nutcrackers, bakers' knives. Examples of the third kind, pincers, tongs, pins, knives, the fore-arm, wings of birds. What is the Roman steelyard? It is a lever of the first kind, and so contrived that one weight may be employed to weigh a great many. Where is the fulcrum placed in it? Near one end, say an inch distant, at this end hang one ounce; if the arm be 16 inches long it will just keep the steelyard in equilibrium. What are the requisites of a good balance? That the arms of the beam ought to be equal in weight and in length and to be as long as their thickness will admit, that the centre of gravity of the system should be a little below the point of support, that the points from which the scales are suspended should be in a straight line with the centre of gravity of the beam, that the axis of motion should be a straight line perpendicular to the direction of the beam, that this axis should be made as

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