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

[elPhys]

Some sources say it's held in a double-bell jar while others say it's a triple-bell jar. What's the scoop?

 

[f95toli]

There is a photo on the BIPM website, so see for yourself

http://www.bipm.org/en/scientific/mass/pictures_mass/prototype.html

 

[elPhys]

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?

 

[lisab]

Free the kilogram! Free the kilogram!11!