Fig. 23.
Your engraving representing “Dynamo Electric Machine with Thomsons Spherical Armature”
—Taken from one of your catalogues, and pasted on a sheet of this paper—
In a system the most important thing next to the dynamo is the lamps. The first experimenter who produced an electric glow was Otto von Guericke. But neither the glow nor electric spark have been used to produce electric light for practical purposes, this was left to the voltaic arc on the one hand and the incandescent lamp on the other. Davy in 1800 mentions experiments in which electric light was obtained by electric sparks between two carbon points. He showed the arc[[4]] light for the first time in 1810 at the Royal Institute, which with Foucalt’s hand regulator (1844) Deleuil lit the Place de la Concorde, Paris. Thomas Wright in London (1845) devised the first apparatus which automatically adjusted the carbons. W. C. Staite used the electric current for the regulation of the carbons in 1848. In 1855 Serrin constructed a lamp which would have been used on a large scale had it not been for the cost of generating electricity. In 1876 Paul Jablochkoff invented his electric candles and in 1881 there were 4000 in use, but as their use increased their defects were found out. Regulated lamps were again brought into use and with them experimenters again endeavored to solve the problem of dividing the electric light. In 1877 Tschikoliff solved the problem in a very simple manner. He reasoned that, if the current be divided and part go through the carbons and make the arc and the rest go through an electromagnet and regulate the arc and the the current unite and when another light is wanted the current be again divided and reunited, the current may be divided any number of times and the scheme work nicely. When put in practice it worked very nicely and is used on most lamps at present. Suppose there be a lamp placed in the circuit. The current divides and the larger half goes through the carbons, as here there is no resistance as the carbons touche, while the remainder, going through a spiral of high resistance, is small. When the carbons burn away a little the arc is formed and the resistance increasing brings the regulating gear into operation. Now the strength of the current is the same after it has gone through the lamp as before because the current is going to get through either one way or the other, hence any number of lamps may go on in series, depending only upon the tension of the current.
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
The Thomson Rice Arc Lamp.
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.
This is when switch F Fig. 22 and M Fig. 24, is turned on. Now since the dynamo will regulate all differences in current the lamps can be turned on or off at will by any one. This is accomplished at the lamp by turning off the switch. When the switch is turned off, the current goes through d to screw K which is then touched by metal L (in contact with binding post B and worked by M).