4.1263 Words: Envelope not on its Edge (1/55)

Elaine Brennan & Allen Renear (EDITORS@BROWNVM.BITNET)
Mon, 22 Apr 91 00:58:32 EDT

Humanist Discussion Group, Vol. 4, No. 1263. Monday, 22 Apr 1991.

Date: Thu, 11 Apr 1991 08:49 MST
From: Sigrid Peterson <SIGPETER@CC.UTAH.EDU>
Subj: The Envelope is not on its Edge

[This posting was lost in the April 11th oddness --ahr]

I first heard the phrase "pushing the envelope" from my father, Hillis
Spencer Peterson, who was an aeronautical engineer in Research and
Design. He used it when I asked him what the sound barrier was. The
envelope is *not* a paper envelope, and it *is* the whole envelope of
air currents as someone has diagrammed. I think originally the sense
was that the airplane pushes this envelope ahead of it until the air
currents interact in an interference pattern so strong that even if the
plane can go faster on its own, it cannot get throughhthis turbulence
created at the speed of sound. The task was then to design planes [and
fly them] that would extend, or push out this protective envelope of air
and keep it there through the sound barrier.

He later talked about test pilots, and mentioned meeting the one who was
famous among all the other test pilots and aeronautical engineers, Chuck
Yeager. Everyone has sort of said all of this before, but it's a bit
less dry than that concluding reference to William Safire, who should
certainly be consulted.

"Edge" also has a performance connotation, in a phrase of its own. A
friend who drove with me when I was younger said I "drove on the edge."
He said that it was a term used by race car drivers meaning to know
exactly the performance capabilities of the car and drive up to them,
but not over them.

Another such phrase is used in psychology, one of my professions, and is
"pushing the limits." One could push the limits of a test's ability to
make distinctions, by getting every answer correct; one could push the
behavioral limits set by authority; one's inclination in a situation
could be to push the limits of whatever could be done; etc.

Not to be confused with "testing the limits," which means that on, for
example, a Stanford-Binet test administered to a child, the child answers
correctly all the questions for hir age: the procedure then is to "test
the limits," or keep asking questions until the answers begin to be

In applications outside their fields of origin, pushing the envelope
then has the connotation of getting through or past a barrier by a
combination of ingenuity and "throw power," another phrase from
aeronautical engineering, this time of rocket power.

Does a given rocket have enough "throw power" to reach escape velocity;
that is, do its rocket motors develop sufficient thrust to push against
the earth so strongly that the rocket will go the other way fast enough
to escape the gravitational pull of earth?.

I hope that helps towards better usage of these phrases.

Sigrid Peterson