Re: A weighty subject

[brian whatcott <inet@INTELLISYS.NET>]

At 16:54 10/15/99 -0400, Michael Edmiston wrote:
> I have a question about the value of g.

> ... there is a thing defined as "the standard g" and this value is
> 9.80665 m/s^2.
>
> Where did this come from?...

> Michael D. Edmiston

What I know:
1) This is the conventional assumed value for Latitude 45 degrees.

2) This value is a defined property of the ICAO Standard Atmosphere
(which is meant to conventionally represent a mid latitude atmosphere.)

3) Montreal is the location of the ICAO -
International Civil Aviation Organization.

4) Montreal observatory is at N45 30 24
5) Montreal g is now given as 9.80652 m s^-2

6) This value (9.80665) was listed in Marks' Handbook (Mech. Eng) 1941
as a standard.

What I speculate:
This value was adopted at a 1924 conference of the International
Union of Geodesy & geophysics as an assumed standard for N45 degrees.




What I  noticed in reviewing these numbers:
Previous errata in writing about g  ...sigh...
I wrote an earlier note which gave a conventional expression for
g with latitude and height. It *should* have shown a term in cos (2 lat)
and one in cos squared (2 lat)  but didn't.

I also wrote a cautionary piece about a barometer that would not show
29.92 in. or  760 mm of mercury at std day conditions.
It read low because the mercury density was increased ( not decreased)
by taking up a vapor from the lab environment.

Sincerely



brian whatcott <inet@intellisys.net>
Altus OK