Place the slit slide into the slide projector. Direct the light from the projector into a prism and observe the spectrum on the screen.  Use three other prisms in the configuration shown to recombine the spectrum.

A common fallacy is that it only take two prisms to do the recombination experiment.  However, if you do this and look closely at the recombined light bar you will see that the edges are red on one side and blue on the other.  This is due to the fact that the light rays coming out of the first prism are spreading out, and therefore the second prism is only able to recombine the central portions of the spectrum.  The two extra prisms are essentially used to take the spreading rays and make them parallel, and then take the parallel rays and refocus them before going into the final prism.