Mind, Body, World- Foundations of Cognitive Science, 2013a

switch was closed matched the durations of the dots and dashes that operated the
relay’s magnet. The ability of a telegraph company to communicate messages over
very long distances depended completely on the relays that were interspersed along
the company’s network.
This dependence upon relays played a critical role in the corporate warfare
between competing telegraph companies. In 1874, the only relay in use in the telegraph
industry was an electromagnetic one invented by Charles Grafton Page; the
patent for this device was owned by Western Union. An imminent court decision
was going to prevent the Automatic Telegraph Company from using this device in
its own telegraph system because of infringement on the patent.
The Automatic Telegraph Company solved this problem by commissioning
Thomas Edison to invent a completely new relay, one that avoided the Page patent by
not using magnets (Josephson, 1961). Edison used a rotating chalk drum to replace
the electromagnet. This is because Edison had earlier discovered that the friction
of a wire dragging along the drum changed when current flowed through the wire.
This change in friction was sufficient to be used as a signal that could manipulate
the gate controlling the circuit between the source and the drain. Edison’s relay was
called a motograph.
Edison’s motograph is of interest to us when it is compared to the Page relay.
On the one hand, the two devices performed the identical function; indeed, Edison’s
relay fit exactly into the place of the page relay:
First he detached the Page sounder from the instrument, an intensely interested
crowd watching his every movement. From one of his pockets he took a pair of
pliers and fitted [his own motograph relay] precisely where the Page sounder had
been previously connected, and tapped the key. The clicking—and it was a joyful
sound—could be heard all over the room. There was a general chorus of surprise.
‘He’s got it! He’s got it!’ (Josephson, 1961, p. 118)
On the other hand, the physical principles governing the two relays were completely
different. The key component of one was an electromagnet, while the critical
part of the other was a rotating drum of chalk. In other words, the two relays were
functionally identical, but physically different. As a result, if one were to describe the
purpose, role, or function of each relay, then the Page relay and the Edison motograph
would be given the same account. However, if one were to describe the physical
principles that accomplished this function, the account of the Page relay would be
radically different from the account of the Edison motograph—so different, in fact,
that the same patent did not apply to both. Multiple realization is the term used to
recognize that different physical mechanisms can bring identical functions to life.
The history of advances in communications and computer technology can
be described in terms of evolving multiple realizations of relays and switches.
Electromagnetic relays were replaced by vacuum tubes, which could be used to
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