Refractive Indexes and Invisibility (A real-life magic trick)

When light refracts from two different substances with the same index of refraction, the materials cannot be distinguished from one another. Here, Pyrex and vegetable oil have the same index of refraction so that the test tube appears invisible in vegetable oil. The light isn’t bouncing off  off of the pyrex tube, just travelling straight through. 

However, water and pyrex have a very different refractive index. The light travelling through the water refracts off the pyrex and reflects back in to your eye, so it does not appear invisible. 

When you see the pyrex test tube under the oil, you are actually just viewing the air inside it before it becomes filled as the pyrex itself is invisible.


The Invisible Man is a science fiction novella by H. G. Wells. Originally serialized in Pearson’s Weekly in 1897, it was published as a novel the same year. The Invisible Man of the title is Griffin, a scientist who has devoted himself to research into optics and invents a way to change a body's refractive index to that of air so that it neither absorbs norreflects light and thus becomes invisible. He successfully carries out this procedure on himself, but fails in his attempt to reverse it.

While its predecessors, The Time Machine and The Island of Doctor Moreau, were written using first-person narrators, Wells adopts a third-person objective point of view in The Invisible Man.