of the former. But transparent stones accord well with all those which interrupt the passage of light by such internal reflections. The diamond, on this account, combines admirably with the cat's-eye and the pearl, but it affords too strong a contrast, especially when of large size, with the turquoise, to associate pleasantly with this nearly opaque stone. From amongst the qualities pertaining to the colour of stones, examples of the utility of the table may be cited. When a stone has much "fire" in it—that is, when its refractive and dispersive actions upon light are high—and it shows prismatic hues, then it looks best if associated with gems in which this property is less developed. Again, monochroic stones, which in all directions transmit beams of the same colour, should be associated with pleochroic stones, which exhibit two or more hues, while the latter should not be mixed together.
We are led from the study of these examples of associations of gem-stones to inquire into the principles which underlie artistic combinations. Probably we are satisfied with arrangements of precious stones in which the leading motif is either identity, or seriation, or contrast. When stones match, when they are graduated, or when they offer a distinct but not startling contrast, the resulting effect is at least capable of being made satisfactory. When we speak of identity, seriation, and contrast, as expressing the elements of decorative association in the mounting of precious stones, we use words into which we are compelled to import special meanings. By identity, we mean that very close resemblance which selected specimens of choice stones of the same kind will exhibit; seriation expresses the orderly sequence of tones or colours with the presence of a pervading and dominant element; contrast implies an effect of change rather than of passage, and may include contrast of tone and of lustre as well as contrast of colour. Instead of further discussing the question of the artistic employment of precious stones in precise accordance with the three principles of association before laid down, a more useful and
