Bauhaus-Universität Weimar

Titel:
Optic Projection: Principles, Installation and Use of the Magic Lantern, Projection Microscope, Reflecting Lantern, Moving Picture Machine
Person:
Gage, Henry Simon and Henry Phelps Gage
PURL:
https://digitalesammlungen.uni-weimar.de/viewer/image/lit39438/544/
536 
THE ELECTRIC ARC 
[Ch. XIII 
The exact nature of the resulting phenomenon will depend upon 
the material of which the electrodes are made, upon the voltage of 
the current supply and the resistance of the rheostat, and the kind 
of gas surrounding the electrodes. 
§ 741. Arc lamp.—Any arrangement for holding the electrodes 
and feeding them together as they wear away may be called an arc 
lamp. 
It consists of three essential elements:—(i) A clamp for holding 
the positive electrode; (2) A clamp for holding the negative elec¬ 
trode; (3) A mechanism for moving the holders and-therefore the 
electrodes nearer together or separating them farther apart. 
The electrode holders must be insulated so that the current must 
flow through the electrodes and not follow any short circuits (fig. 
270). 
For the hand-feed and the automatic types of arc lamps see 
Chapter I, § 9-11. 
§ 742. With direct current, the arc is made up of three parts. 
1. The arc stream; a highly heated, incandescent gas which 
conducts the current between the electrodes. 
2. The positive crater; where the current leaves the positive 
electrode to enter the arc stream. 
3. The negative crater; where the current leaves the arc stream 
to enter the negative electrode (fig. 292). 
§ 743. Electrical behavior of the direct current arc.—Measure¬ 
ment of the voltage drop in various parts of the carbon arc reveals 
the fact that the potential difference between the two electrodes 
(§ 743a) is made up of three parts. Starting from the positive 
side, the potential difference between the positive electrode and the 
arc stream is about 32 volts. The potential difference between the 
arc stream and the negative electrode is about 9 volts, thus the 
potential difference between the electrodes with the shortest possi¬ 
ble arc is about 41 volts (§ 743b). 
As the arc is lengthened there is an additional drop in potential 
in the arc stream which depends mainly on the length, but partly on 
the cross section of the arc stream. As the arc length is changed,
        

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