. The telephone system of the British post office. A practical handbook . onstruction. The south pole of the permanent magnet is immediately above thecentre of the armature, thus rendering the centre north and both endssouth. The electro-magnet is joined up in the ordinary way; thus acurrent in one direction flowing through it will cause A to become northand B south. The armature is repelled at B and attracted at A, thusholding the hammer upon the right dome. Reversal of the current makesA south and B north; the armature is therefore attracted at B and repelled Magneto Bells. 45 at A, the resu
. The telephone system of the British post office. A practical handbook . onstruction. The south pole of the permanent magnet is immediately above thecentre of the armature, thus rendering the centre north and both endssouth. The electro-magnet is joined up in the ordinary way; thus acurrent in one direction flowing through it will cause A to become northand B south. The armature is repelled at B and attracted at A, thusholding the hammer upon the right dome. Reversal of the current makesA south and B north; the armature is therefore attracted at B and repelled Magneto Bells. 45 at A, the result of which is that the hammer passes over to the left handdome. It will be seen that a succession of currents in opposite directionswill cause the hammer to vibrate between the two domes, thus giving aring. Adjustment of the play of the armature is made by moving thedomes bodily, screws for that purpose being provided. The distancebetween the armature and the electro-magnet is adjustable within smalllimits by means of the nuts on the screwed pillars of the frame Figure 35. The external appearance of a magneto bell is shown in Figure 35. Itsresistance is now 1,000 , though formerly many of lower resistances, 100 ■*to 500 , were used. The high resistance bells require far less current,and in a large exchange this is an important matter, as the pulling upof the generator is very serious. During the busy hours of the day thegenerator would almost stop were ioom bells universal, and it is obviousthat the lower the speed of the generator the less is its , and thusmany of the bells would not be rung at all. In order that the principle ofthe magneto generator may be clearly comprehended, it will be well to referback to the theory of the induction coil. It has previously been statedthat whenever a conductor is cut by magnetic lines of force generated in that conductor. It would, however, be more accurate tosay that whenever the number of lines of force passing
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Keywords: ., bookcentury1900, bookdecade1900, booksubjecttelepho, bookyear1901
