COLORADO RIVER, or COLORADO OF THE WEST, a large river rising in Utah, and flowing s. and w. through Utah and Arizona, and between Nevada and 'California and Arizona. The Colorado is formed by the junction of the Green and the Grand rivers of Utah in lat. 38° north. The main tributaries of the Colorado arc from the c., and include the San Juan, the Little Colorado, and the Gila. After leaving United States territory, the Colorado flows s. between the Mexican provinces of Lower California and (1.110ra, and discharges its waters into the extreme n. point of the golf of California.. The length of the Colorado, reckoning from the sources of Green river, is about 2000 miles. It is navigable for steamers a little over 600 in., nearly to the foot of the Grand Cai1011. There is a good harbor near the mouth of the river, used mainly by vessels in the Colorado trade. The remarkable features of this river are its canons, which extend for more than 500 In. along its course. The most notable, and in itself a great wonder, is more than 200 in. long, with walls quite or nearly vertical, varying from 4,000 to 7,000 ft. high. The channel of the river is in some places 100 yards wide, and then perhaps, suddenly narrowed to less than 20 yards. The fall of the stream is from 5 to 200 ft. m a mile. and the deep gloomy gorge is full of whirlpools and waterfalls. Below the canons there is a valley from 2 to S m. wide, of fertile soil. In 1867, the canons were descended by James White, the sole survivor of a party prospecting for mines. Ho escaped through them from hostile Indians, and floating on rafts of driftwood, came out scarcely alive. Again, in 1869, prof. J. W. Powell, with a corps sent by the United States government, explored the canons through their whole length, suffering great hardships, and often narrowly escaping with life.
a term introduced by sir David Brewster to denominate a defect of vision, owing to which certain persons are either unable to discern a single color, such as red, or to distinguish between two colors, such as green and red, so that they may be said to be blind to red, or to be blind to one of two colors presented simultane ously to the eye. This defect has been called false vision of colors; Daltonism, after Dalton the chemist, who suffered under it; and various other learned names, have been applied to it; but color-blindness seems to be as apt and expressive a name as any. It occurs in eves whose power of vision, as to form and dis tance, is otherwise perfect. The late Dr. George Wilson, whose work on this subject should be consulted by the reader (Researches oeColor-blindaess, Edin. 1855), thus classi fies the varieties of the defect: 1. Inability to discern any color properly so called, so that black and white—i.e., light and shade—are the only variations of tint perceived. 2. Inability to discriminate between the nicer shades of the more composite colors, such as browns, bays, and .neutral tints. 3. Inability to distinguish between the primary colors, red, blue, and yellow, or between these and the secondary and tertiary colors, such as green, purple, orange, and brown. The first sort would appear to be very rare, but well-marked cases of it are on record, and show that insensibility to colors is not only compatible with distinct vision in other respects, but is frequently attended by a greater power than is usual of perceiving objects very faintly illuminated. None of
these recorded cases, however, have been examined with such care as to warrant the conclusion that the color-blindness was absolute. It would appear that where the color blindness is nearly absolute, degrees of luminosity supply the place of shades of color in giving variety to the aspects of objects. The second variety of color-blindness, where the nicer shades of the more composite colors are mistaken, would appear to be very common—the rule rather than the exception in the majority of persons, at least of the male sex, in this country; but it is a matter of doubt how far it may not be referable to imperfect cultivation of the sense of color. In many cases of this kind, however, it can be shown that the defect differs in degree only from that of the third form. The third form is the most important variety of the affection. In extreme cases, although colors are occasionally quite correctly named, there is no certainty as to any color: in less severe cases, two colors, at least, as red and green, and generally four, as red, green, olive, and brown, are not distinguished from each other. Yellow would appear to be the color which gives least difficulty to those not absolutely unconscious of color; while blue, if pure and well illuminated, is readily recognized by the color-blind, a few of whom, indeed, describe it as the color which they see best. Red appears to be the color the want of the sense of which may be said to characterize all the color-blind. Indeed, Dr. Wilson thinks color-blindness might properly enough be called anmithric (no-red) vision. He says that while the normal eye analyzes white light into three colored ele ments, one of which is red, the color-blind eye, on the other baud, analyzes white light into two elements, neither of which is red.
The eyes of persons having this defect of vision have been carefully examined after death without the discovery of any peculiarity. Colorblindness therefore has its scat in the sensoritun, not iu the visual apparatus.
Color-blindness would appear to be very prevalent. Of 1154 persons, of various pro fessions, examined in 1852 and 1853 at Edinburgh by Dr. George Wilson, 65, or 1 in 17.7, were color-blind; 21 confounded red with green; 19 confounded brown with green; and 25 confounded blue with green. In consequence of this prevalence of the defect, the investigations into its nature are of the greatest practical importance! Railway ofli dials, for instance, should always be tested for it, lest, being color-blind, they should mistake the various signals in use on lines of rail, and thus cause accidents.
Sir David Brewster, sir John Herschel. prof. Maxwell, and many others, have written on the subject of color-blindness. Perhaps the most ingenious investigator of color-blindness, and the phenomena of vision generally, is prof. Maxwell, whose writings thereon in the Transactions of the Royal Societies of London and Edinburgh, will well repay perusal.