NATURAL PHILOSOPHY. 199 



that we can make with wood -which we leave of the color which is peculiar 

 to it, as ebony, its brown color permits its employment with light stuffs to 

 produce contrasts of tone rather than contrasts of color. We can also 

 employ it with very brilliant, intense colors ; such as poppy, scarlet, aurora, 

 flame-color, &c." 



The following subtleties may be useful to men in trade : 

 " First Fact. When a purchaser has for a considerable time looked at a 

 yellow fabric, and he is then shown orange or scarlet stuffs, it is found that 

 he takes them to be amaranth- red, or crimson, for there is a tendency in 

 the retina, excited by yellow, to acquire an aptitude to see yiolet, whence 

 all the yellow of the scarlet or orange stuff disappears, and the eye sees 

 red, or a red tinged with violet. 



Second Fact. If there is presented to a buyer, one after another, four- 

 teen pieces of red stuff, he will consider the last six or seven less beautiful 

 than those first seen, although the pieces be identically the same. What is 

 the cause of this error of judgment ? It is, that the eyes, having seen seven 

 or eight red pieces in succession, are in the same condition as if they had 

 regarded fixedly during the same period of time a single piece of red stuff ; 

 they have then a tendency to see the complementary of red ; that is to say, 

 green. This tendency goes of necessity to enfeeble the brilliancy of the 

 red of the pieces seen later. In order that the merchant may not be the 

 sufferer by this fatigue of the eyes of his customer, he must take care, 

 after having shown the latter seven pieces of red, to present to him some 

 pieces of green stuff, to restore the eyes to their normal state. If the 

 sight of the green be sufficiently prolonged to exceed the normal state, the 

 eyes will acquire a tendency to see red ; then the last seven red pieces will 

 appear more beautiful than the others." 



* 



ON COLOR OF THE WATER OF THE MEDITERRANEAN SEA. 



The usual tint of the Mediterranean Sea, when undisturbed by acci- 

 dental or local causes, is a bright and deep blue ; but in the Adriatic a 

 green tinge is prevalent ; in the Levant Basin, it borders on purple ; while 

 the Euxine often has the dark aspect from which it derives its modern 

 appellation. The clear ultramarine tint is the most general, and has been 

 immemorially noticed, although the diaphanous translucence of the water 

 almost justifies those who assert that it has no color at all. But notwith- 

 standing the fluid, when undefiled by impurities, seems in small quanti- 

 ties to be perfectly colorless, yet in large masses it assuredly exhibits tints 

 of different intensities. That the sea has actually a fine blue color at a 

 distance from the land cannot well be contradicted ; nor can such color 

 however influential the sky is known to be in shifting tints be considered 

 as wholly due to reflection from the heavens, since it is often of a deeper 

 hue than that of the sky, both from the interception of solar light by the 

 clouds, and the hues which they themselves take. This is difficult to 

 account for satisfactorily, as no analysis has yet detected a sufficient quan- 



