Why.......Spirit Level.......?

Factual Questions
1

  1. Why does the bubble in a spirit level always go to the centre of the vial when the vial is dead horizontal ? Presumably if the vial is horizontal, the bubble should have no consistant preference for a locus anywhere along the length of the vial. (I would think)

  2. Why does the bubble remain near the centre of the vial when the spirt level is nearly horizontal ? Presumably the bubble of air should simply continue to rise to the high end of the vial. (I would think)

2

Because the walls of the vial are slightly curved.

3

The curvature in the vial is such that the center is the high spot, with the ends being lower.

4

If this is true, then the level would only read properly on one edge; set on the other edge the bubble would run to an end. Mine registers properly on both edges. Perhaps the tube is just slightly swelled in the middle, rathaer than being curved?

SWAG alert!
As to the name “spirit level”, I would guess that refers to alcohol in the tube rather than water. Alcohol would not foster life or freeze where water might. I don’t know what’s in there now, but I suppose it’s possible that alcohol was the original fluid.

5

The vial is a slightly larger diameter in the middle than it is on either end.

So no matter how you rotate the vial around it’s long axis, the middle is always higher than either end as long as the vial is very close to horizontal.

As you move the vial off of horizontal, the slight tilt overcomes the bulge in the middle of the vial, and bubble moves toward the higher end.

I remember years ago having a level where the vial was simply curved, and it only worked with one specific edge up. So it had 4 vials, each one curved toward one edge. Not as handy as the bulging vial variety, but usable.

6

i.e. it is barrel shaped with a circumferential profie.

There is also a “Bullseye” level to level a horizontal surface in all directions at once. It has a spherical surface and small circle target for the small bubble.

7

If you reflect upon it for a moment, you’ll see that what I wrote is true of a vial that is swelled in the middle (as well one such as you envisioned).

8

Sorry, GaryT… I jumped to the conclusion that you meant a macaroni shape. Come to think of it, I think I have seen one like that. My mistake…

Anyone got any input on the “spirit” part? Mine was just a guess.