Origin of the Term Vertical Angles

Date: 04/04/2005 at 10:56:32
From: Neil
Subject: Vertical angles

Why do we call them "vertical angles" when many of them are
"horizontal" (extending left and right)?  Where did that name come from?

Date: 04/04/2005 at 12:38:54
From: Doctor Peterson
Subject: Re: Vertical angles

Hi, Neil.

They're called "vertical angles" because they share a "vertex".

The confusion comes in because the Latin word "vertex" got into math 
by two different routes.  A vertex originally meant the top of the 
head, or the summit of a hill.  That led, on the one hand, to the idea
of a corner of a figure, such as the apex of a pyramid, being called a 
vertex; and on the other hand, to anything at the top--like the 
highest point in the sky--being called vertical.  So although vertical 
angles have nothing to do with being upright, and vertical lines have 
nothing to do with having a corner, we end up with the same word in 
both places.

If you have any further questions, feel free to write back.

- Doctor Peterson, The Math Forum
  http://mathforum.org/dr.math/ 

Date: 04/04/2005 at 12:47:44
From: Neil
Subject: Thank you (Vertical angles)

Dear Dr. Peterson, 

Thank you so much for your answer to the "vertical" angle origin.  I
wish I had asked you that years ago.  I will use your answer from now
on when I am teaching about vertical angles.

 - Neil (in my 40th year of teaching secondary math)