Volume 5 — Miscellany.

New Electric Machines.—At the conversazione given by the president of the Royal Society at Burlington House, London, the display of newly constructed astronomical, optical, and other philosophical instruments afforded a gratifying proof of improvements in the mode of construction, and of increased skill on the part of the constructors. The large spectroscope, which is to be used in combination with Lord Rosse's monster telescope, was a triumph of workmanship and of philosophical adaptation of means to ends; and we may expect ere long to hear of important discoveries in spectroscopic phenomena. Mr. C. W. Siemens and Professor Wheatstone exhibited each one a remarkable electric machine of his own invention, which demonstrated in a surprising way the convertibility of mechanical force into electricity. In these machines, a bar of soft iron, wrapped lengthwise in copper wire, is made to rotate between two other bars of soft iron, which are fixed. The rotating bar is inoculated, so to speak, with a small touch of magnetism, and then being set spinning very rapidly, the small touch is generated into a stream of electricity, which passes off with a crackling noise, increasing or diminishing in proportion to the rotation. In a laboratory, such a machine would be highly serviceable, as it could be used to generate large quantities of electricity very cheaply, and there is no doubt but that many other ways of turning it to account will be discovered. Mr. Siemens has already discovered one most important way, namely, the lighting-up of buoys and beacons at a distance from the shore, by sending a current of electricity to them through a submarine cable. That is the way in which he purposes to employ the electricity generated by his machine: his method has been approved by the Commissioners of Northern Light-houses, who intend to apply it to light the buoys and beacons that mark the most dangerous spots round the coast of Scotland. But of all wonderful electric machines, the one invented by Mr. H. Wilde of Manchester is the most wonderful. A machine which weighs about four and a half tons, including one ton of copper wire, and which requires an eight-horse steam-engine to keep its armature in rotation, must necessarily produce tremendous effects. It gives off electric fire in torrents: the light produced is intense, and is quite as useful to photographers as sunlight, with the advantage over the sun, that it can be used on dark days and at night. This light, as we hear, is already employed in manufacturing establishments, and is to be introduced into light-houses. A French company, who have purchased the right to use it in France, will try it first in the light-house on Cape Grisnez, whence, as is said, the light will radiate not only all across the Channel, but some distance into the southern counties of England. Besides the production of light, the new machine is applicable to important manufacturing purposes; the size of the machine being altered to suit special circumstances. A well-known firm at Birmingham are about to use it, instead of a galvanic battery, for the deposition of copper on articles required to be coated with that metal. In this case, the electricity of the machine is substituted for the acid and zinc of the battery, and will cost less. In another instance, the machine is to be used for the production of ozone in large quantities for employment in bleaching operations. Professor Tyndall exhibited the sensitive flame, on which he had given a lecture at the Royal Institution: or, to be more explicit, he made experiments to show the action of sound on flame. The results are remarkable. A tall flame, looking like an ordinary gas-flame, issuing from a circular orifice in an iron nipple, behaves in an extraordinary way when, by increased pressure, it is raised to fourteen or sixteen inches in length. If a shrill whistle be blown in any part of the room, it suddenly drops down to about half the length, and rises again immediately on cessation of the sound. A blow of a hammer on a board produces a similar effect; and still more so when the blow is on an anvil: the flame then jumps with surprising briskness, the reason being that the ring of the anvil combines those higher tones to which the flame is most sensitive. So tuning-forks, at the ordinary pitch, produce no effect; but if made to vibrate one thousand six hundred, or two thousand, or more times in a second, the flame responds energetically. In another experiment, a fiddle is played in presence of a flame twenty inches in length—the low notes produce no effect; but when the highest string is sounded, "the jet," to quote Professor Tyndall's own words, "instantly squats down to a tumultuous bushy flame, eight inches long." And the same effect is produced by strokes on a bell at twenty yards' distance: at every stroke the flame drops instantaneously. This last experiment is a good illustration of the rapidity with which sound is propagated through air, for there is no sensible interval between the bell-stroke and the shortening of the flame. Another flame, nearly twenty inches long, is yet more sensitive, for the rustle of a silk dress, a step on the floor, creaking of boots, dropping of a small coin, all make it drop down suddenly to eight inches, or become violently agitated. At twenty yards' distance, the rattle of a bunch of keys in the hand shortens the flame, and it is affected even by the fall of a piece of paper, or the plashing of a raindrop. To the vowel U, it makes no response; to O, it shakes; E makes it flutter strongly; and S breaks it up into a tumultuous mass. Many more instances might be given, but these will suffice to show that surprising effects are produced by sound. To the scientific inquirer they will be serviceable as fresh illustrations in the science of acoustics. Chambers's Journal.