Kilogram in France: Double-Bell or Triple-Bell Jar?

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The discussion centers on the confusion regarding the containment of the kilogram prototype, specifically whether it is housed in a double-bell jar or a triple-bell jar. Participants reference a photo from the BIPM website, which may clarify the current setup. There is speculation about the historical context of the prototype's housing, suggesting it may have originally been in a double-bell jar before an additional jar was added. Some contributors propose that the outer jar may not qualify as a true bell jar due to its lack of a knob, leading to differing interpretations of the setup shown in Halliday and Resnick's third edition. The conversation emphasizes the need for clarity regarding the prototype's housing and its historical evolution.
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Some sources say it's held in a double-bell jar while others say it's a triple-bell jar. What's the scoop?
 
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There is a photo on the BIPM website, so see for yourself:approve:

http://www.bipm.org/en/scientific/mass/pictures_mass/prototype.html
 
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But in the third edition of Halliday and Resnick it shows a picture of it in what appears to be a double bell jar.

So is there some history I'm missing? Was it originally in a double bell jar and then another bell jar added later?

Or maybe the outer "bell jar" isn't considered by some to be a true bell jar (since it doesn't have a knob at the top), and the Halliday and Resnick photo was zoomed into take a picture of just the inner two jars?
 
Free the kilogram! Free the kilogram!11!
 

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