<p>A <a href="https://en.wikipedia.org/wiki/Spirit_level" rel="nofollow noreferrer">spirit level</a> is an instrument used to find a horizontal or vertical plane. In surveying, the spirit level is used as a reference. Surveying instruments like the <a href="https://en.wikipedia.org/wiki/Theodolite" rel="nofollow noreferrer">theodolite</a> have a spirit level built in. This is used to set up the instrument, after which you can measure angles relative to that reference plane.</p>
<p>This makes sure you have a repeatable reference, and not one that depends on the incline of the local surface.</p>
<p>As to the origin of the name:</p>
<p>it's called a <em>level</em> because it is used to find a level surface (i.e. one that's horizontal). It's called a <em>spirit</em> level because the liquid inside is usually a spirit (i.e. a mix of alcohol and water).</p>
<blockquote>
<p>Early tubular spirit levels had very slightly curved glass vials with constant inner diameter at each viewing point. These vials are incompletely filled with a liquid, usually a colored spirit or alcohol, leaving a bubble in the tube. They have a slight upward curve, so that the bubble naturally rests in the center, the highest point. At slight inclinations the bubble travels away from the marked center position. Where a spirit level must also be usable upside-down or on its side, the curved constant-diameter tube is replaced by an uncurved barrel-shaped tube with a slightly larger diameter in its middle.</p>
<p>Alcohols such as ethanol are often used rather than water. Alcohols have low viscosity and surface tension, which allows the bubble to travel the tube quickly and settle accurately with minimal interference from the glass surface. Alcohols also have a much wider liquid temperature range, and won't break the vial as water could due to ice expansion. A colorant such as fluorescein, typically yellow or green, may be added to increase the visibility of the bubble.</p>
</blockquote>
<p>why &quot;<a href="https://en.wikipedia.org/wiki/Liquor#Etymology" rel="nofollow noreferrer">spirit</a>&quot;:</p>
<blockquote>
<p>The term &quot;spirit&quot; in reference to alcohol stems from Middle Eastern alchemy. These alchemists were more concerned with medical elixirs than with transmuting lead into gold. The vapor given off and collected during an alchemical process (as with distillation of alcohol) was called a spirit of the original material</p>
</blockquote>

CC BY-SA 4.0
2019-04-27T12:54:15.840Z
My question is why is it called "spirit level" not how we use it. I am curious on what is the meaning/origin of the term
Jim
CC BY-SA 4.0
2019-04-27T12:59:53.690Z
spirits = alcohol. It's just a vial of alcohol with a bubble in it.
Ingolifs
CC BY-SA 4.0
2019-04-27T13:39:15.987Z
@uhoh: Yes. I updated the title. I am sorry for the confusion
Jim
CC BY-SA 4.0
2019-04-27T13:41:09.873Z
@Hobbes: Thank you for the details. They explain the term in regards to the specific tool. But I have heard also the term being used outside of any usage of a tool. In the post I mention I heard it as part of the sentence: ` the sun's shadows is X degrees to the plane of the spirit level...` which seems to me that the same term is used to signify something else too. Unless the term is used also with the meaning of a location that is flat and can be verified with the tool you explained
Jim
CC BY-SA 4.0
2019-04-27T13:59:51.587Z
@Jim looks great, thanks!
uhoh
CC BY-SA 4.0
2019-04-27T14:08:55.100Z
@Jim By the way the instrument works, the plane of the spirt level can also be described as the plane perpendicular to the local (combined) gravitational accelaration.
Hagen von Eitzen
CC BY-SA 4.0
2019-04-27T15:04:48.657Z
@HagenvonEitzen: I see. Is this standard terminology or sometimes used? Has this term long history of usage?
Jim
CC BY-SA 4.0
2019-04-27T15:56:17.667Z
@Jim: It is more technically precise than saying "horizontal". Even if you're making your observations at a place where you can see the ocean so there's a good _horizon_ to sight towards, if you're at any significant elevation the curvature of the earth begins to create errors. Just 25 meters above sea level, the true horizon will be about ten arcminutes _below_ the spirit level. (Atmospheric refraction complicates this further).
hmakholm left over Monica
CC BY-SA 4.0
2019-04-27T11:15:26.263Z
2019-04-27T13:25:00.677Z
2020-06-17T09:47:40.653Z
Hobbes
<p>I have heard the term "plane of the spirit level" e.g. the sun's shadows is X degrees to the plane of the spirit level to signify the surface of the earth and I see it is a common term used in surveying and as an instrument to show if there is a curvature.<br>
My question is: where is this term coming from?</p>

<earth><history>
What is the origin of the term "plane of the spirit level"?
Jim
# What is the origin of the term "plane of the spirit level"?

(Asked by: username_0 on 2019-04-27)

I have heard the term "plane of the spirit level" e.g. the sun's shadows is X degrees to the plane of the spirit level to signify the surface of the earth and I see it is a common term used in surveying and as an instrument to show if there is a curvature.  
My question is: where is this term coming from?

**Tags:** earth, history

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## 1 answers

### Answer by username_1 on 2019-04-27. Score: 3 | Accepted answer

A [spirit level](https://en.wikipedia.org/wiki/Spirit_level) is an instrument used to find a horizontal or vertical plane. In surveying, the spirit level is used as a reference. Surveying instruments like the [theodolite](https://en.wikipedia.org/wiki/Theodolite) have a spirit level built in. This is used to set up the instrument, after which you can measure angles relative to that reference plane.

This makes sure you have a repeatable reference, and not one that depends on the incline of the local surface.

As to the origin of the name:

it's called a *level* because it is used to find a level surface (i.e. one that's horizontal). It's called a *spirit* level because the liquid inside is usually a spirit (i.e. a mix of alcohol and water).

> Early tubular spirit levels had very slightly curved glass vials with constant inner diameter at each viewing point. These vials are incompletely filled with a liquid, usually a colored spirit or alcohol, leaving a bubble in the tube. They have a slight upward curve, so that the bubble naturally rests in the center, the highest point. At slight inclinations the bubble travels away from the marked center position. Where a spirit level must also be usable upside-down or on its side, the curved constant-diameter tube is replaced by an uncurved barrel-shaped tube with a slightly larger diameter in its middle.
>
> Alcohols such as ethanol are often used rather than water. Alcohols have low viscosity and surface tension, which allows the bubble to travel the tube quickly and settle accurately with minimal interference from the glass surface. Alcohols also have a much wider liquid temperature range, and won't break the vial as water could due to ice expansion. A colorant such as fluorescein, typically yellow or green, may be added to increase the visibility of the bubble.

why "[spirit](https://en.wikipedia.org/wiki/Liquor#Etymology)":

> The term "spirit" in reference to alcohol stems from Middle Eastern alchemy. These alchemists were more concerned with medical elixirs than with transmuting lead into gold. The vapor given off and collected during an alchemical process (as with distillation of alcohol) was called a spirit of the original material

> **Comments:**
> **username_0**: My question is why is it called "spirit level" not how we use it. I am curious on what is the meaning/origin of the term  
> **username_2**: spirits = alcohol. It's just a vial of alcohol with a bubble in it.  
> **username_0**: @uhoh: Yes. I updated the title. I am sorry for the confusion  
> **username_0**: @Hobbes: Thank you for the details. They explain the term in regards to the specific tool. But I have heard also the term being used outside of any usage of a tool. In the post I mention I heard it as part of the sentence: ` the sun's shadows is X degrees to the plane of the spirit level...` which seems to me that the same term is used to signify something else too. Unless the term is used also with the meaning of a location that is flat and can be verified with the tool you explained  
> **username_3**: @Jim looks great, thanks!  
> **username_4**: @Jim By the way the instrument works, the plane of the spirt level can also be described as the plane perpendicular to the local (combined) gravitational accelaration.  
> **username_0**: @HagenvonEitzen: I see. Is this standard terminology or sometimes used? Has this term long history of usage?  
> **username_5**: @Jim: It is more technically precise than saying "horizontal". Even if you're making your observations at a place where you can see the ocean so there's a good _horizon_ to sight towards, if you're at any significant elevation the curvature of the earth begins to create errors. Just 25 meters above sea level, the true horizon will be about ten arcminutes _below_ the spirit level. (Atmospheric refraction complicates this further).  

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