Final answer:
A vacuum inside a glass enclosure allows for minimal air resistance and a controlled environment, which is crucial for experiments where air interference must be eliminated, for protection of contents, and for maintaining temperature via insulation.
Step-by-step explanation:
The glass enclosure maintains a vacuum inside the tube, which allows for minimal air resistance and a controlled environment. For example, in the Davisson-Germer experiment, the use of a vacuum chamber is essential to prevent air molecules from interfering with the electron paths, thereby ensuring that the results are attributable solely to the interactions of interest. Similarly, gas discharge tubes utilize a vacuum to allow electrons within the gaseous atoms to get excited and emit light without collision with air molecules, producing the distinct colors characteristic of these tubes. Additionally, a vacuum is employed in thermos bottles or Dewar flasks to minimize heat transfer through convection and conduction, maintaining the temperature of the contents for an extended period. During changes of state, as when a gas is sealed in a flask to be condensed into a liquid, a vacuum can prevent external air from affecting the process, ensuring correct measurement of properties like mass or pressure.