On Thu, 02 Jul 2015 15:32:06 +1000, Peter Moylan wrote:
> No bolas in sight. The entry for "parabola" is less clear, but there I
> can see the "para" as referring to being parallel to the side of the
> cone.
Usually you guys are better than that, so, I didn't supply my
references.
A "bola" is certainly part of the word, where "bola" comes from
the Greek/Latin roots for the weapon of a string with two weights
on the end.
Even Wikipedia has this, so, I was pretty sure you guys would
get the reference (since most of you are smarter than I am).
A very nice question, for the answer of which you have to look into
ancient
Greek.
The verb from which "parabola" is derived is "paravallo" (the last letter
actually being an "omega", more or less pronounced as an o. The v of
ancient
Greek is changed to a b, as often done when a word is borrowed in English,
following the Erasmian pronunciation).
Now, the verb "paravallo" comes from the preposition "para", roughly
meaning "from", "near", "against" and the verb "ballo" . This last has a
spectrum of meanings, but the one relevant here is "to compare". All in
all,
"paravallo" means roughly "to place close for comparison" .
Naturally you will ask what is the relevance to mathematics. Here it is:
In Euclid's celebrated geometry text, the Elements, there is a geometric
construction that asks to construct a rectangle on a given side and of
given
area. The wording there uses the verb "paravallo" in the sense that it is
required to produce a rectangle comparable in area to a given one.
This became in antiquity the standard terminology. Later it was taken up
by Apollonius in his celebrated book of Conic sections (of which the
parabola is an example). There, when he proved the property (in modern
notation) y^2 = a*x, he wrote that the area y^2 is comparable (in the
above
sense) to the rectangle whose one side "a" is given. Thus he called the
curve he was studying "a parabola". This is the name that survived up to
our
time, replacing the old name " section of a rectangular cone" used by its
inventor Menaechmos.
When Apollonius studied the curve now called a hyperbola, he proved that
for a similar comparison of areas, one of the two "exceeded". In his
terminology, it was "hyper" (meaning "larger"). Thus he coined the term
"hyperbola", roughly meaning "the one that exceeds in comparison",
replacing
its old name " section of an obtuse angled cone".
For the ellipse, the same area "fell short", in other words, "was
elliptic"
.
You are, then, right. The ellipse could be called "hypobola", only that
this word has a different meaning in Greek, and so perhaps was not
preferred.
Once into linguistics, I take the opportunity to mention the etymology of
a few other words in English that come into my mind, whose root is the
same
verb "vallo" in Greek. The reason I am doing this, is because the average
person does not realize that these words are related.
- Anabolic: from the preposition "ana" and the verb "vallo" . Its original
meaning being "to lift, to elevate" , from which the anabolics that
athletes use to improve their strength.
- Diabolic: from the preposition "dia" and the verb "vallo". Its original
meaning being "to slander, to calumniate", from which the devilish act.
- Metabolic: from the preposition "meta" and the verb "vallo". Its
original
meaning being "to alter", from which the action of metabolism, i.e. change
of a situation.
That's all then. As you see, "bola" comes in parabolic, hyperbolic,
anabolic, diabolic, metabolic and elsewhere.
All the best from hot Crete.
Michael Lambrou.