Incandescent lamps were produced as early as 1859 but not till 1879 when Swan, Edison, Sawyer and others were they ever in a practical form. The first glow lamp Edison constructed had platinum wire to be heated. He however examined the properties of organic substances and finally fixed on bamboo fibre. The bamboo is divided into fibres one millimeter in diameter and twelve millimeters long. These fibres are pressed in U-shaped moulds and baked in ovens where they are allowed to become carbonized. The carbonized filament is attached to platinum wires which are fused in a glass vessel from which the air has been exhausted. We will speak more fully of the incandescent lamp when describing the Thomson Houston System’s incandescent lamp.
The Thomson Arc lamps was used by the Thomson Houston System since its begining till about two years ago when they stopped manufacturing them, only furnishing broken parts. The arc lamps at present used is
They are manufactured in two styles the single lamp used for stores, buildings etc., and the double lamp used for street service, all night work, etc. The light is produced by the voltaic arc between two carbons, the negative pole or lower carbon burning away about half as fast as the positive pole or upper carbon. The outside view of the single lamp is seen in Fig. 21 and of the double lamp in Fig. 22.
The regulation of the double lamp is diagramatically shown in Fig. 24, which is a plan of the lamp with cover removed, showing only a plan of cylindrical part of the lamp. The wires marked _a b c d_ run along the top in order to be out of the way. In Fig. 24 the current comes in at the binding post and is at _A_ divided into three currents _A_, _B_, and _C_. The current _a_ goes to the yoke _I_ of the electromagnets _h_ and _i_ and when the yoke is not held down by magnets _h_ and _i_, it goes out wire _a_ to binding post _B_. This only continues a moment until the current _b_ which goes through the carbons and at the start has almost no resistance offered it, attracts the yoke _I_ thus breaking contact of curcuit _a_ until the current ceases or till both carbons burn away, when in the latter case the resistance of _b_ becoming very high as compared to _j_ and _k_ but little current goes through _h_ and _i_ and _I_ is raised by a weak spring not shown, thus making contact of circuit _a_, and since current _a_ has little resistance as compared to _b_ or _c_ most of the current goes through it, thus practically making a cut-out. The current _b_ goes round the electro-magnets _h_ and _i_, then to the “bed” through screw J, the “bed” being a cast iron bottom of the cylinder _E_ Fig. 22. From the bed it goes down carbon holder _C_ (or _H_) through carbons and arc to frame bed _A_ Fig. 22. From there it comes up a wire by the side of frame _C_ Fig. 22 and joins other currents at _B_. The third current _a_ goes through electromagnets _j_ and _k_ and joins other currents at _B_.