It will be perceived that any disorder in a lamp cannot affect other lamps in the circuit and will right itself or if not the lamp can immediately be switched out of circuit.
Now as to the regulating gear. The two carbon holders are held up, H, by clutch operated by springs (not shown) till end N of lever ON is permanently held down, and C, by the raising and falling of yoke D. There is only one arc burning at a time in a double lamp and the so-called positive carbon C burns first. When the lamps are trimmed the switch is first turned off the carbons put in and the switch turned on. This will draw the upper carbons up about a quarter of an inch.
When the current is turned on the circuit aa is almost instantly broken and most of the current goes through c as the distance between carbons being a quarter of an inch the arc has a very large resistance. The electromagnets j an k attract D which lets loose C, which falls to lower carbon, and the resistance being almost nothing, most of the current goes through b. This weakens j and k which lets D up while D takes C up with it thus establishing the arc. The current all goes down C till the enlarged end of C strikes lever ON thus letting H drop and also putting it in electrical contact with “bd,” which it was not in before. After a short time the carbons burn away, the arc becomes longer and establishes itself and the resistance becoming greater in passing from carbon to carbon and a correspondingly less current flows through b and a greater one through c. This makes the electro-magnets j and k strong enough to draw D to them in spite of spring Q. When D is attracted by j and k, C (or H) falls and again the arc lengthens, always being kept about 3/32 inch long. This is frequently and continually repeated, the delicacy depending upon the strengh of the spring Q as compared to the electromagnets strength.
Fig. 24.
When the carbon in carbon holder C burns to a length of about two inches in attempting to fall to maintain arc’s length, an enlarged port at the top of the carbon holder C strikes and holds down lever ON pivoted at O (and end N held up by a spring P) thus letting loose a clutch by which electrical contact is made between H and “bed” and letting H fall till it touches lower carbon when an arc is established and regulated just as for C.
The Thomson-Rice single lamp has the same gear with the exception of having only carbon holder C, H, lever ON, and spring clutch and spring P being absent. The single lamp will burn eight hours and the double lamp fourteen hours continuous running.
These lamps are intended only for a steady current and will not cut out of circuit if the current gets too strong. But with the Thomson Houston dynamo the current never gets too strong and because of this there are less power absorbing mechanism and as anything’s functions decrease the remaining functions are increasedly better. As the Thomson-Rice lamp has less functions and power consuming machinery, it can but be the most economical, delicately adjusted and steadiest lamp extant. They are made to stand a current of five amperes above the normal current for a short time, as, when forty lights are simultaneously cut out of a forty-five light circuit, the current runs up about four amperes above the normal current for about one half a minute.
Prof. Thomson has gotten out a divided arc lamp which supplies a light of moderate candle power for locations where a 2000 candle power lamp gives more light than can be economically utilized. It is specially suited for factory and mill use where looms or other tall machines are liable to cast disadvantageous shadows. It is said that these lights are supplied cheaper per candle power than the standard lamp and up to date is sucessful.
He has also arranged apparatus by which arc lamps are run in multiple series, series or multiple arc. It is said that divisions, redivisions and reunions are practicable. This is also sucessful as far as we can find out.