NavList:

For an artificial horizon trough the size they were normally made (and for a Davis one)you need about 750 grams of mercury (I've just filled one until the bottom is uniformly covered while weighing it on the kitchen scales).

If you use water, blacken the interior of the trough, but a liquid that is already black is better. I used old sump oil when I experimented thirty years ago and found it excellent, though on windless nights I took successful star shots off the surface of a swimming pool (blue liner). Cooking oil with added food dye is cheap, doesn't smell like sump oil and is easier to clean off clothing. If you paint the interior of a large metal oven roasting dish black and make a 6 mm hole in one corner about 30 mm up from the bottom, you have a bigger area for picking up the reflection of the body and it is easier to pour the oil back into its container. The depth of the dish provides some protection from the wind.

Thick modern float mirror glass can be used in a frame with levelling feet, but you need a sensitive level to set it up, preferably one with a sensitivity of about 30 seconds per 2mm bubble movement. Such levels are not cheap, but if you can obtain the vial alone, you can set it up on a home made base yourself with a bit of Plasticene. I ground the interior of the vial in the attachment o a barrel shape and made flats on the brass end caps to stop it from rolling around.

Bill Morris
Pukenui
New Zealand
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