few pieces of drift wood, and, having secured their arms and provisions, commenced their downward journey on the night of Aug. 24. Subsequently the raft was generally secured by night and allowed to drift only during the day. On the 28th, while descending a cataract, Strole was drowned, and all the provisions were washed overboard. White continued the journey alone, amid great peril from cataracts, rocks, and whirlpools, hemmed in by the walls of the cañon, and 10 days after reached Callville, having tasted food but twice during that period. Once he obtained a few green pods and leaves from bushes growing along the stream, and the second time he was given some food by Yampais Indians who occupied a low alluvial strip of land along the river, the trail to which from the plateau was known only to themselves. In 1869 a corps fitted out by the United States government, under the command of Prof. J. W. Powell, started in boats from the upper Green river in Wyoming territory, and, after much peril and many hair-breadth escapes, reached Callville, having passed through the whole length of the cañons. In 1871 another expedition under Prof. Powell was fitted out for the exploration of the Colorado valley. The portion of the river embraced in this exploration is about 1,000 m. in length, commencing where the Union Pacific railroad crosses Green river, and extending down the stream to the end of the Grand cañon. E. and S. of the river the survey runs back from 10 to 40 m. from the stream. On Jan. 1, 1873, the exploration had been completed of the region N. and W. of the Colorado, drained by its tributaries, from the Rio Virgen on the south to the Dirty Devil on the north, embracing a territory 300 m. long and 175 m. wide. N. of this a general reconnoissance had also been made of the territory between the Wasatch mountains and San Pete valley on the west and Green river on the east, embracing the valley of the Uintah, the ranges of mountains and extensive plateaus lying S., the valley of Price river, the Wasatch plateau, the valley of the San Rafael, and the plateau and mountains in which this river has its sources. The survey of the region embraced in Prof. Powell's plan is to be completed in 1875, when the entire valley of the Colorado will have been explored, the portion above the Union Pacific railroad and that below the Grand cañon having been already surveyed.
COLORADO, or Cobn Leubu, a river of the Argentine Republic, rising in the Andes about lat. 35° S., and flowing S. E. across the pampas through an imperfectly known country to the Atlantic, which it enters in lat. 39° 51′ S., lon. 62° 4′ W.; length about 600 m. By some authorities it is supposed to receive the waters of the Mendoza and the Desaguadero, which drain the great system of lakes in San Luis and Mendoza. It discharges through several mouths, the principal one having two fathoms of water at low tide. It is obstructed seaward by shifting sand banks. The tide rises at its mouth from six to nine feet. It is said to be navigable only about 120 m.
COLOR-BLINDNESS, a curious defect in vision, depending on a want of sensibility in the eye, or perceptive capacity in the brain, in consequence of which certain colors are not distinguished, or all colors are alike invisible as such. It is believed that attention was first called to this defect by the publication by Dr. Dalton, the distinguished chemist, in 1794, of the particulars of his own case. The name given to the affection is that proposed by Dr. George Wilson, from whose work on the subject (Edinburgh, 1855) the following summary is chiefly condensed. It has also been called Daltonism. A cause for the lateness of the discovery of this phenomenon may be found in the fact that while the ignorant would not investigate a disability of the kind under which they might labor, the educated and intelligent would learn to compensate for it by the use of other senses. No mention of color-blindness has been found in ancient or modern writers up to the period named; but the examples of the affection already collected are numerous, and among its subjects were Dugald Stewart and Sismondi, contemporaries of Dalton. The difficulty shows itself in three forms or degrees: 1, in an inability to distinguish nicer shades and hues, such as grays and neutral tints; 2, in inability to distinguish certain primary colors from each other, as red from green, or these from secondary or tertiary hues, as scarlet, purple, &c.; 3, in inability to discern any color as such, the person seeing only white and black, lights and shades. In the first degree, this affection is, among males, rather the rule than the exception. Dr. Wilson found that of 1,154 persons examined by him in Edinburgh, more than one in 18 were in a greater or less degree color-blind; and that of 60 persons in the chemical class of the Edinburgh veterinary college, the majority declined to name any colors beyond red, blue, yellow, green, and brown; while they failed entirely in attempting to arrange nearly related hues of yarns or stuffs, or those of varying shades of the same hue. He found that pink and other pale colors, especially pale yellow and blue and green, were often confounded. The same thing happened with orange and yellow, lilac and bluish gray, <fec. In the second degree, in the less marked cases, red and green, or these with olive and brown, fail to be distinguished. And it is apparently singular that colors among the most distinct to a normal eye are in these cases the most easily confounded, red and green being more readily so than yellow and purple; while green is in these respects the most delinquent of all the colors. Dugald Stewart could not distinguish the red fruit of the Siberian crab from the green color of its leaves. Three brothers, Harris, mistook red for green, orange for grass green, yellow for light green. A tailor at Plymouth regarded the solar spectrum as consisting only
