. L'ère pharmaceutique. c champ créé par les pôles de l'électro-aimant apowerful. Les deux principaux types d'armature sont l'armature à anneau Gram et l'arniature à tambour Siemens. L'armature de Gram se compose d'un anneau en fer avec un fil isolé de telle sorte que la bobine sans fin de fil formsan. (Fig. 103.) L'armature du tambour est un cylindre en fer enroulé sur une longueur de fil de cuivre isolé, également dans une bobine sans fin.(Fig. Loi.) Deceniboi- 0. 1807.] L'ERA PHARMACEUTIQUE. 873 lorsque l'une ou l'autre de ces arniatiies isturned entre les tliepoles d'un aimant acurrent est mise en place inone direction dans lhuile de

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. The Pharmaceutical era. c field created by the poles of apowerful electro-magnet. The two chief types of armature are the Gramme ringarmature, and the Siemens drum arniature. The Gramme armature consists of an iron ring woundwith insulated wire in such a way that the wire formsan endless coil. (Fig. 103.) The Drum armature is a cylinder of iron wound length-wise with insulated copper wire, also in an endless coil.(Fig. lOi.) Deceniboi- 0. 1807.] THE PHARMACEUTICAL ERA. 873 When either ofthese arniatiiies isturned between tliepoles of a magnet acurrent is set up inone direction in thecoil of one side ofthe armature, andanother in the oppo-site direction iu theportions of the coilon the other side.These currents areconducted to metal-lic surfaces on theaxle of the armatureand are here takenofE by means ofpieces of copperknown as brushes, which form the con-nections with theoutside circuit. Fig.105 exhibits appear-ance of finish dyna-mo with drum ar-mature. The electro-mag-net which producesseparately excited by. the armature with the brushes in such a way that wheathe current reverses iu the armature, the commutatoralso reverses its connection with the brushes, so that the+ current always Bows out through one brush and the— current through the other, no matter what the direc-tion may be in the coils. The Electric Motor.—In tlie dynamo the current is pro-duced by causing a conductor to revolve in a magnetic-field, and the development of electric energy is propor-tional to the mechanical energy required to revolve thearmature against the resistance offered by the lines offorce. The dynamo, then, is simply a device for the con-version of mechanical into electrical energy. This proc-ess can also be reversed, for if a current generated byone dynamo is passed in through the brushes of another, the armature of the latter will be caused to revolve, butin a direction opposite to the armature of the machinefrom which the current comes. It is customary, there-fore, to say th

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