Murphy's Law

humour (Or "Sod's Law") The correct, *original* Murphy's Law

reads: "If there are two or more ways to do something, and one

of those ways can result in a catastrophe, then someone will

do it." This is a principle of defensive design, cited here

because it is usually given in mutant forms less descriptive

of the challenges of design for lusers. For example, you

don't make a two-pin plug symmetrical and then label it "THIS

WAY UP"; if it matters which way it is plugged in, then you

make the design asymmetrical (see also the anecdote under

magic smoke).

Edward A. Murphy, Jr. was one of the engineers on the

rocket-sled experiments that were done by the US Air Force in

1949 to test human acceleration tolerances (USAF project

MX981). One experiment involved a set of 16 accelerometers

mounted to different parts of the subject's body. There were

two ways each sensor could be glued to its mount, and somebody

methodically installed all 16 the wrong way around. Murphy

then made the original form of his pronouncement, which the

test subject (Major John Paul Stapp) quoted at a news

conference a few days later.

Within months "Murphy's Law' had spread to various technical

cultures connected to aerospace engineering. Before too many

years had gone by variants had passed into the popular

imagination, changing as they went. Most of these are

variants on "Anything that can go wrong, will"; this is

sometimes referred to as Finagle's Law. The memetic drift

apparent in these mutants clearly demonstrates Murphy's Law

acting on itself!

[Jargon File]

(1998-02-14)