>>So what is the Fresnel lens of the first order ?
;and how did it differ from the third order?
  could not the same candle power be seen at further distance because of 
the
refraction of the light in the cut of the  glass  lens and not the actual
candlepower ?<<

I assessed conditions at Monhegan Light, 12 miles off the coast of 
Maine, last fall, and learn something, thought not all, about lights.

The higher order lenses displayed the light over a greater square area 
at the lens, with the same amount of light and a larger lens it 
increased the distance from which they can be seen.

I was amazed to learn that the modern optic at Monhegan Light has  only 
a 24volt 15watt electric bulb and can be seen 18 to 20 miles at sea, I 
thought they blazed with thousands of watts, but not so. The actual 
source of the light can be marginal, it's the optic that "throws" the 
light. The island folks talk about when they were kids they didn't have 
to carry flashlights as they walked about the island at night, they 
would just wait for the light to swing around to the path, then walk 10 
or 20 feet as the light passed by, then stop and wait for the light to 
swing around again--ahhh island life. I did not get enough so I'm taking 
my wife back there the first week of Sept., we'll take the mail boat out 
from Port Clyde, south of Thomaston, Maine--can hardly wait, 5 days of 
island life. (we get to stay in the cottage that Rockwell Kent built 
with his own hands in 1906.)

John (lucky dog, lucky dog) Leeke

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