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Pàgina 372 - This last bed of lava must have been brought to a state of the most perfect liquefaction, as it had filled up every crevice that was more than half an inch wide. It appeared highly glazed, and in some places we could discover small round pebbles from the size of a hazel nut to that of a hen's egg, of the same colour, and having the same...
Pàgina 79 - This red ray appears to possess a definite refrangibility, and to be characteristic of the salts of potash, as the yellow ray is of the salts of soda, although, from its feeble illuminating power, it is only to be detected with a prism. If this should be admitted, I would further suggest, that whenever the prism shows a homogeneous ray of any colour to exist in a flame, this ray indicates the formation or the presence of a definite chemical compound.
Pàgina 78 - ... presence of the substance, which suffers no diminution in consequence. Thus a particle of muriate of lime on the wick of a spirit-lamp will produce a quantity of red and green rays for a whole evening without being itself
Pàgina 79 - The flame of sulphur and nitre contains a red ray which appears to me of a remarkable nature. This red ray appears to possess a definite refrangibility, and to be characteristic of the salts of potash, as the yellow ray is of the salts of soda, although, from its feeble illuminating power, it is only to be detected with a prism.
Pàgina 79 - For instance, the orange ray may be the effect of the strontia, since Mr Herschel found in the flame of muriate of strontia a ray of that colour. * If this opinion should be correct and applicable to the other definite rays, a glance at the prismatic spectrum of a flame may show it to contain substances, which it would otherwise require a laborious chemical analysis to detect.
Pàgina 365 - The direction of the magnetic polarity of small needles exposed to an electric current directed along a wire stretched longitudinally, varies with the distance of the wire :"—the action being found to be periodical with the distance. M. Savary observed three periods, and also the fact that the distances of maximum effect and of the nodal zeros " vary with the length and diameter of the wire, and with the intensity of the discharge.
Pàgina 275 - The travellers reached the elevation of 15,500 feet, where the pass appeared to be 1,400 or 1,500 feet higher, over vast fields of snow. The dell is broad (half a mile wide), and covered with snow in high wreaths. The mountains, which have a SE exposure, are nearly bare, a few patches of snow only appearing at great heights. The line of cliffs may be 17,500 feet. On the other side, the mountains are nearly of the same height, and they present a chain of mural precipices, eaten away by frost into...
Pàgina 107 - ... as it is required to make the course of the instrument go faster or slower than the motion of the heavens ; and- if once placed, it may be kept in that position by returning the hand to its original position. The same mechanism is also used to make the motion of the instrument coincide with that of the sun and moon. This instrument has four eyeglasses, the least of which magnifies 175 times, 'and the largest 700 times.
Pàgina 339 - To take advantage of the propelling power of gunpowder, as is done with a cannon-ball, only reversing its mode of action, and instead of a spherical, to apply one of a conical form, by which the full effect of the wedge is given in every direction at the lower part of the charge, but particularly downwards. 3. And, in the...
Pàgina 279 - The travellers had to pick their way : one while upon smooth surfaces of granite, sloping to the raging torrent ; at another, the route led among huge masses and angular blocks of rock, forming capacious caves, where fifty or sixty people might rest : here the bank was formed of rough gravel, steeply inclined to the river ; there the path was narrow, with a precipice of 500 or 600 feet below, whilst the naked towering peaks, and mural rocks, rent in every direction, threatened the passenger with...