In article , Bob Mannix
wrote:

"John Cartmell" wrote in message
...
In article , Bob Mannix
wrote:

"John Cartmell" wrote in message
...
In article , Dave Page
wrote:
The Natural Philosopher wrote:
Lobster wrote:

When topping up old insulation (Rockwool) it's normal and more
effective to lay the second layer perpendicular to the first.

I think you mean 'orthogonal'

Perpendicular is walls... ;-)

I understood what Lobster meant, and feel that "perpendicular" was
quite appropriate. After all, laying insulation foam vertically
wouldn't make sense.

'Perpendicular' without the sense of vertical makes no sense at all.
What would it be hanging (-pend-) from?

Yes it does. It only implies vertical in some of its meanings
(architecture, physical landscape) and not in others (maths and the
conjunction of two lines or planes).

AFAIK it should only be used in maths & drawing where it's used to
represent a physical verticality.

Oh no, definitely not - two lines in maths/geometry perpendicular to each
other are usually representing no physical reality at all but are always
described as perpendicular

No.
You have to define the horizontal plane first. Of course that may only be
assumed but, if you have assumed a line across the page to be the horizon and
the top of the page as up, then a line at right angles to the first line is
perpendicular to it *because you have defined the first line as the horizon*.
In lazy maths today we generally forget that we have implicitly made that
initial assumption.

Where you are describing a physical (3 or more dimensions) situation
'perpendicular' cannot mean horizontal.

It cannot *mean* horizontal per se, I agree, but could be used to describe
things which form lines at right angles in some arbitrary plane (which
might be horizontal) by considering them merely as geometric concepts. If
the information being conveyed included information on verticality then
perpendicular would clearly mean vertical.

You can indeed make any arbitrary plane the horizontal plane. In the case in
hand you are saying that you have assumed that a vertical plane through the
house is the horizontal plane.

Can we please return to reality before the thought makes me sea-sick! ;-)

A quote from Round the World in Eighty Days:

"It was supplied with two rows of seats, perpendicular to the direction
of the train on either side of an aisle which conducted to the front and
rear platforms."

The translator made an error.

That one's for a rainy day, I fear, not having a French copy to hand )

http://www.fourmilab.ch/etexts/www/tdm80j/tdm80j.html

;-)

--
John Cartmell john@ followed by finnybank.com 0845 006 8822
Qercus magazine FAX +44 (0)8700-519-527 www.finnybank.com
Qercus - the best guide to RISC OS computing