prisms, producing a very strong appearance of colour with a very moderate refraction, and presenting the effect which we have called hyperchromatism in a very vivid manner.
685.
In common glass, the alkaline nature obviously preponderates, since it is chiefly composed of sand and alkaline salts; hence a series of experiments, exhibiting the relation of perfectly alkaline fluids to perfect acids, might lead to useful results.
686.
For, could the maximum and minimum be found, it would be a question whether a refracting medium could not be discovered, in which the increasing and diminishing appearance of colour, (an effect almost independent of refraction,) could not be done away with altogether, while the displacement of the object would be unaltered.
687.
How desirable, therefore, it would be with regard to