Now retired, I recently witnessed a demonstration called “Frozen Hands” that made me wish I were still in the classroom. The demo employs the sameness of the index of refraction of glass and a liquid. For years I charmed students by breaking test tubes and placing the broken fragments into a clear liquid (usually chlorobenzene or vegetable oil, both of index 1.5). Unknown to the class, I placed beforehand two test tubes in the beaker of liquid. Since the test tubes have the same index of refraction as the liquid, the tubes are “invisible.” The reason I submerged two test tubes is because the students always, and I do mean always, ask me to do it again. I then present the “trick” to the class and state that a new liquid has been invented that can put together broken glass. I will demonstrate this feat by showing a glass test...

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