The Montgomery advertiser., 1901-08-09
ELECTRICAL ENGINEERING
 By Arthur E. Watson, A. M.
ARTICLE W.
Dynamos for Incandescent Lamps.

Dynamos for Incandescent Lamps.
 Incandescent lamps are commonly arranged in multiple-each has an in- dependent connection with the source of current. Two wires are led rom the dynamo as faf as the most remote lamp auC the lamps are connected across like the rounds of ladder. Whatever current passes through one lamp does not go through any othe' this method is just the opposite or the arc current, for !r that the same cur ren: goes through al the lamps III series, Were incan6escent lamps con nected in series dangerously nlgn potentials would be brought within easy reach, a large number ofeeparate circuits would be nee led to providS Tor the thousands of lamps to be lighted the breaking of one lamp would inter- rupt a whole circuit and the dyna'nos could not accommodate the varying de- mands of the separate circuits.
 The incandescent lamp system IS somewhat like a water or gas system. Bach faucet or jet represents an ln- dependent outlet: the reservoirs or tanks are to keep, as nearly as possi- ble "a uniform pressure throughout the extending piping and to supply quan- titles varying with the demands. A
  a definite voltage, suitable for the lamps. upon the whole network of wires; though no lamp be burning there must always be the readiness Of | the current as soon as the key is turned. Even though large numbers of lamps be lighted the volume of current must be in measure corre-' spending; though accidental short circuits happen there must be kept up the same pressure; in its attempt to supply excessive demands there might more current flow than would be the capacity of the wires of the dynamo to withstand or the power of the engine might be insufficient, hence safety fuses are inserted in numerous places in the various branches to melt and confine the injury to an inexpen- sive device and prevent a general in- terruption of the entire system.
 Instances of operating incandescent lamps in series are offered in the case of street carS-five 1l0-volt lamps being in series on the regular 5oO-volt troll ley supply, and in cases of some street lamps forty twenty -five-volt lamps be- ing connected in series on regular 1,000-volt alternating current dynamos. Even in these cases, there are large number of such groups connected inde- pendently to the dynamos, so these in- dividual circuits are really in multiple.
 Edison was pioneer in incandes- cent lighting, being contemporary with Brush in arc lighting. At first his dynamos were separately excited, later and for many years he employed ordi- nary shunt wound field magnets: regu- lation as to proper potential was ef- fected manualy by use of a variable resistance or rheostat in the field cir ciut: during light loads considerable resistance is inserted in this circuit, thereby weakening the fields at full load nearly all the resistance is cut out. and the magnets are fully excited Early forms of field magnets were very long and slender, later, after Hopkinson had formulated the law of the mag netic circuits the entire line of dynames was redesigned, having magnets about | one half as long. and of twice as great cross section; this alteration having taken place in 1885 the machines are | commercially known as the 'S5 type. One of these is shown in figure 35.
 Electric generators are commonly | rated in kilowatts; the watts equal the product of the volts by the amperrs and 1000 watts equal one kilowatt, 746 watts equal oe horse power; then a kilowatt equals about one and one l InlTQ horse power. ne cut S1bWS q 100 k. W. size: since one sixteen candle power lamp requires about fifty watts. the lamp capacity of any dynamo can easily be determined.
 The current capacity of any dynamo
 is purely matter of the size of the wire. and some data regarding wires will be appropriate. A wire is com monly round not square. so system of measurements of areas in round or circular measure has been devised. A wire 001 inch diameter is called of one "miu" diameter-derived from Latin word denoting thousand; the area of cross section of such wire is called one circular mill a circular mil is as much smaller in area than a square mil as circle is similar in area than its circumscribed square. Ordinary safe limits of temperature are reached in dynamos under 20 k. W. sizes, when 300 circular mils per ampere is allowed for an armature wire and 1000 circular mills per ampere for a field winding Larger machines, in which the wire Is