. The Boston school compendium of natural and experimental philosophy .. . n passing through it; w^hich, touching the mercury on the inside,is also in contact with the wire that proceeds outwards, on that sideof the instrument On the other side of the instrument, b, the thickcopper wire, soon after turning down terminates, but a thinnerpiece of wire forms a communication between it and the mercuryon the cup beneath. As freedom of motion is regarded in thewire, it is made to communicate with the former by a ball andsocket joint •, the ball being held in the socket by a piece of thread ;or else,
. The Boston school compendium of natural and experimental philosophy .. . n passing through it; w^hich, touching the mercury on the inside,is also in contact with the wire that proceeds outwards, on that sideof the instrument On the other side of the instrument, b, the thickcopper wire, soon after turning down terminates, but a thinnerpiece of wire forms a communication between it and the mercuryon the cup beneath. As freedom of motion is regarded in thewire, it is made to communicate with the former by a ball andsocket joint •, the ball being held in the socket by a piece of thread ;or else, the ends are bent into hooks, and the one is then hooked tothe other. As good metallic contact is required, the parts shouldbe amalgamated, and a small drop of mercury placed between them;the lower ends of the wire should also be amalgamated. Beneath the What illustration is given ? What does fig. 131 represent ? Explain the figure ?How is the freedom of motion, which is required on the wire, obtained ! Howcan the metallic contact, which is required, be obtained ? 17. 186 NATURAL PHILOSOPHY. hanging wire, a small circular magnet is fixed in the socket of thecup b, so that one of its poles is a little above the mercury. As inthe former cup, a metallic connexion is made, through the bottom,from the mercury to the external wire. If now the poles of a battery be connected with the horizontalexternal wires, c, c, the current of electricity will be through themercury and the horizontal wire, on the pillar which connectsthem, and it will now be found, that the moveable part of the wirewill rotate around the magnetic pole in the cup b, and the magneticpole round the fixed wire in the other cup a, in the direction beforementioned. By using a very delicate apparatus, the magnetic pole of the earthmay be made to put the wire in motion. Fig. 132 represents another ingenious contrivance, invented byM. Ampere, for illustrating the electro-magnetic rotation ; and ithas the advantage of com
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Keywords: ., bookcentury1800, bookdecade1830, booksubjectphysics, bookyear1837
