. Railway and locomotive engineering : a practical journal of railway motive power and rolling stock . cur-rent, as the magneto had done, but forthe fact that the armature was built withwhat has been called a commutator forthe purpose of producing a direct currentfrom the alternating current generated,that is, current in which the flow is al-ways in one and the same direction. Infact, it may be said generally, that alldynamos deliver alternating current, butthe intervention of the commutator causesthe alternations to become a steady flowin one direction. This brings us to the consideration ofw
. Railway and locomotive engineering : a practical journal of railway motive power and rolling stock . cur-rent, as the magneto had done, but forthe fact that the armature was built withwhat has been called a commutator forthe purpose of producing a direct currentfrom the alternating current generated,that is, current in which the flow is al-ways in one and the same direction. Infact, it may be said generally, that alldynamos deliver alternating current, butthe intervention of the commutator causesthe alternations to become a steady flowin one direction. This brings us to the consideration ofwhat is a commutator. It is, roughlyspeaking, a device for converting an al-ternating current into a continuous a sort of convenient way of present-ing to the mind the winding of an arma-ture of the Siemens type, let us look atthe way a fisherman might be expected towind up a long line on a piece of woodenshingle taken from the roof of a house,and notched out into a rough V at eachend. Say he began with the rod-end ofhis line and wound it back and forwardover the notched shingle. When it was. FISHING LINE WOUND UP. all wound up the line at the rod-endmight be covered by all the other turnsof the line, and the hook-end would comeoff on top and hang free. Now, supposethat it was possible to send some kind ofmolecular impulse along this fishline, itwould begin, say, at the free end, and goin along the hook and finally come out atthe rod-end after having traversed allthe intermediate coils. A similar im-pulse entering the line at the rod-endwould rapidly traverse all the coils of fish-line and come out, off the hook-end. Thatwould practically be equivalent to an al-ternating current, and here the commu-tator steps in and produces a continuouscurrent from these two which have flowed through the line in different di-rections. A glance at the outline sketch willshow a pair of commutator bars as twooblong strips of metal attached to thearmature wires. These single wires rep-resen
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