Andrew Janssen wrote:

> The website I got a lot of heliograph information from is:
> 
> http://myweb.cableone.net/kd7aoi/
> 
>  From the pictures of the American Service heliograph and the British 
> Mance heliograph, it seems pretty clear that the mirrors are in fact 
> flat.

The American Service heliograph is a drawing, not a photograph.  The British 
and Portuguese heliographs are clearly parabolic.  Look at the circular 
patterns on the reflective surfaces.  A flat mirror would show either lines or 
waves.

> There's also a reference under one of the subsidiary links to the 
> American heliograph, 4in mirror, being bright enough to hurt the naked 
> eye at forty miles away.

Then it has to be parabolic.  Ordinary reflected sunlight is not dangerous at 
that range.

Jefferson
http://www.picotech.net/~jeff_wilson63/rpg/



----------------------------------------------------------------
To unsubscribe, send mail to celandra-off@phoenyx.net.