Relationship between length and diameter of contact bridge formed under thermal equilibrium condition

From the authors' investigations on the initial instantaneous phenomena in breaking contacts, we have found the two types of bridge, i.e. one is a brightened (luminous) bridge and another one is a dark (non-luminous) one. This paper discusses on the dark bridge formed between contacts when the separation speed is very small. The following items are mentioned in this paper: a) bridge model and theory on the relationship between bridge length and diameter. b) thermal flow from bridge to its vicinity, c) deduction of a thermal equilibrium condition from the calculation of thermal flow time constant. d) experimental works, e) discussions and f) conclusions. In conclusion, we see the coincidence of the tendency of the theory and experiment carried out on the relationship between bridge diameter and length.