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Examples of solutions to the problem of leading an electrical current through the wall of a vaccum vessel.

The fact that metals typically have much larger thermal expansion coefficients than glass make sealing a copper wire through glass problematic.

However, special alloys and special glasses have been developed to overcome this problem. Some of the examples here represent the first step in the construction of a valve. The central glass tube can be used as a support for the electrode structure while the other end  is used to evacuate the tube after the bulb has been sealed on.