Cabinet Incubator..newbie question

[AussieAcres]

Ok, so I am doing a little research and brainstorming on ideas for building my own cabinet incubator. I see a lot with a mason jar inside filled. What is this for? I would assume humidity...but it is sealed...I am lost?!?!?

 

[quintinp]

it is for steady temps,,, if you have a lot of eggs at a certain temp, and you also have the mason jars filled with water it will keep the temp from dropping or going to high when the thermostat goes on and off..... if you have a homemade incubator,,, most people use a water heater thermostat, and this thermostat fluctuates 6 degrees in temp, so jars of water are needed in some cases,,,..

 

[AussieAcres]

Ok..I think I understand. It is a passive heat regulator. Absorbing the heat while the light is on and radiating heat while it is off?