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OT: refilling a spirit level bubble.

This is on an Abney Level , a simple surveying instrument for taking levels around a site or off a datum. Over time the bubble enlarges and so less and less accurate sighting of the centre of the bubble. This one , the glass cylinder is cemented in a brass holding barrel. One end , where molten glass is somehow sealed over the contents of the cylinder, is accessible. Breaking away the cement at that end , probably broke away the glass , or maybe had fractured with temp or vibration, causing the large bubble to form. Anyway easy to refill vertically using a hypodermic syringe. But how to seal up, as still recessed inside the brass cylinder. I'm thinking of a drop of nail varnish over the full to the brim spirit. Then a few more layers of nail varnish to build up a bit. I'm hoping there will be enough "dissolved" air to settle out and form a bubble. Anyone done this or similar, or any hints?

Reply to
N_Cook
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Given the need for absolute accuracy - otherwise the instrument is entirely useless - you may want to replace it entirely. Then there is re-installation and calibrating. I 'came up' on on optical transits... fun.

Peter Wieck Melrose Park, PA

Reply to
pfjw

Calibration is the easy bit, a 5km professional laser-levelled pair of fixed points locally about 150m apart. A few layers of nail varnish worked , for today, but I somehow doubt itwill be long-term reliable. Surveyed to a benchmark 100m away, to obtain the height, wrt Ordnance Survey datum. GPS , even dGPS is a waste of space in comparison to optical or laser levelling to good old benchmarks.

Reply to
N_Cook

Unless you have a warm air layer in between refracting your line of sight.

Reply to
Tim R

I reckon a blob of silicon would complete the seal.

Reply to
Rheilly Phoull

I might try that next time. The resultant bubble was a bit larger than I'd have liked, so next time leave to settle for a few hours, before topping up with spirit and then sealing over. I should say I've no access to a pro laser level and sensing staff but when there were anti-flood measures put in place locally, I got them to place a nail in the flood wall at a specific height relative to a distant specific level. Otherwise presuambly a matter of going to the coast , Abney placed near a calm sea edge and sighting the horizon.

Reply to
N_Cook

Working near a very, very hot room and opening the doors to the cold, cold outside can cause that visual effect.

Reply to
bruce2bowser

There is a rather famous case where tunnels were supposed to meet from each side of a mountain, but didn't. Analysis showed they'd relied on a laser level, and it had been bent by a warm air layer in the path.

Reply to
Tim R

Any surveyor can calibrate quickly with no instrumentation. Set level tripo d almost exactly between two objects approximately 200ft apart. Make a mark on each object (rotate 180deg back and forth). Said marks will be exactly at the same elevation. Move level (4-5ft) close to one mark, sight it, rota te to second mark (200ft away) and hope to read the same relationship. Adj ust bubble accordingly, and repeat entire procedure.

Reply to
Ivan Vegvary

I think that imaging using electromagnetic radiation or waves has come quite a ways, too.

Reply to
bruce2bowser

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