Can anyone direct me to a source which explains how the mercury bearing for a lighthouse functioned?

Mercury bearings involve the weight of the object "floating" on a rather small amount of mercury. I say "floating" because the bearing normally involves a matched pair of hollow cylinder case and inserted cylinder post. The post carries the object and the case holds the mercury. Often the "post" was donut shaped so the case looked like a round race track. A mechanical bearing keep them centered. The space between them was quite narrow, 1/8" or so. When under load, the mercury went across the bottom of the case and up the sides between them, applying a force just to the bottom just the same as if there was a huge puddle of mercury with a boat in it of the same displacement. Mercury 30" deep provides a force of almost 15 pounds per square inch so if the case was just over 30 inches deep and the bottom area was 30" across and 5" wide (392.6 sq inches) it could support about 5890 pounds. A 1000 pound lens system would take a rise of about 6"

Here is a plan http://www.southsolitaryisland.com.au/userimages/L... but the slot for the mercury bearing has to be almost divined out at the rim, I believe - copy the image to a photo processing or viewing software where you can enlarge it even more (IE8 automatically reduces it to fit, but clicking will enlarge) This is the source http://www.southsolitaryisland.com.au/page9.htm which discusses the head on this and a linked page to the lantern which gives dimensions.