Understanding the Mechanics of Galileo Temperature Gauges

[Lrdmora]

Okay, this is not for homework, just curious. I was at a friends this weekend and he had a Galileo temperature gauge. I was trying to figure it out.

It is full of glass bubbles that are half full of liquid, some small, some large, with glass weights at the bottom and markers.

As the temperature rises the liquid in the oval bubbles becomes less dense.

Heres my first question: If the liquid becomes less dense what causes it to fall? My belief from placing it near the fire place and watching it, is that as the volume of the liquid increases it compresses the air or gas in the bubble making it less bouyant. (The liquid actually rises to above the halfway mark when hot) Will someone set me on the correct path?

My second question: I noticed that the bubbles were different sizes. And that they fall at different temperatures. Are the bubbles filled with different liquids that react at different temperatures, or are the weights of the bubbles different with the same liquid.

I know this is an elementary question, but I sure would appreciate any answers to appease my curiousity.

Thanks a ton.

 

[chroot]

http://www.hewgill.com/galilean-thermometer/

- Warren

 

[Lrdmora]

I guess I am missing a basic thing.

Thanks for the link! But I am slow today.

How does the density of the object decreasing make it weigh more? I thought increasing the density would make it heavier? What am I missing?

 

[HallsofIvy]

I think you've misunderstood. It is not the liquid in the "bubbles" that becomes more or less dense, it is the liquid that is supporting them.
The "bubbles" themselves are rigid. There volume does not change, of course, the mass does not change, so the overall density remains the same (the density of the gas or liquid inside each "bubble" is irrelevant- since the overall volume does not change, neither does the overall density.
The "bubbles" are made with more or less glass so that the density of each one is the same as density of the supporting liquid at some specific temperature. When the liquid reaches a given temperature, all "bubbles" with density greater than that of the liquid at that temperature sink.

 

[Lrdmora]

Thank you!

That makes a lot more sense! I guess I was being a little dense myself, heh, heh.

Thanks for taking the time to explain something elementary to me.