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 where all the white light which falls upon the house is absorbed except the red, and all which falls upon the grass is absorbed except the green.

The mixture of colors is a very complicated subject, but the student will find it very lucidly treated in Captain Abney's little ^book: Color Mixture and Measurement in the Romance of Science Series; as also in Shelford Bidwell's Curiosities of Light and Sight.  Colorado is located in the center of that portion of the United States west of the Mississippi River. The state is quadrilateral in shape; and is bounded by Wyoming and Nebraska on the north, Nebraska and Kansas on the east, Oklahoma and New Mexico on the south and Utah on the west.

Area. The state is about 370 miles long and 280 miles wide, while the gross area of the state is 103,948 square miles. Deducting a few small lakes and other bodies of water leaves 103,658 square miles of land area. Colorado is larger than Great Britain, half as large as France, and nearly equal in area to New York, Pennsylvania, New Jersey and Delaware combined.

Mountains. The continental range of the Rocky Mountains extends across the state from north to south near its center. Pike's Peak, west of Colorado Springs, is the most famous peak in the state, but not the highest, it being one of many that have an elevation of 14,000 feet to 14,500 feet.

The surface of Colorado has two natural divisions,—mountains and plain. The mountain-division has an altitude from 5,000 feet to 14,000 feet. The plain-division is from 4,000 feet to 5,000 feet high.

Rivers. The principal rivers of the eastern slope are the South Platte and the Arkansas. The Rio Grande drains the San Luis valley. The Grand flows toward the southwest. The Yampa and White are tributaries of the Green, which unites with the Grand in eastern Utah and forms the Colorado River. None of these rivers is navigable. These rivers with their numerous branches furnish a supply of water for irrigation purposes.

Climate. The climate is delightful; the air is dry, the sunshine abundant. There are rains throughout the warm parts of the year and snows in winter, but both are moderate in quantity. The altitude and dryness minimize the heat in summer and the cold in winter. The perpetual-snow line varies between 13,000 and 14,000 feet, except on the side of the mountains sloping to the north and in deep canyons where it is lower.

Mineral Springs. There are more than seventy-five groups of mineral springs having medicinal properties. The most noted ones are located at Manitou, Canon City, Idaho Springs, Glenwood Springs, Hot Sulphur Springs, Steamboat Springs, Pagosa Springs, etc.

Land. The report of 1911 of the Commissioner of the United States General Land-Office, Washington, D. C., shows that 20,599,100 acres of government land were unappropriated and unreserved, of which 19,069,624 acres had been surveyed and 1,529,476 acres had not been surveyed. Since the date of that report there have been many entries by settlers on such lands. When Colorado was admitted to the Union, Congress granted to the state two sections of land in every township for the support of the public schools.

The soil on the uplands is a rich, sandy loam, varied in some localities by clay or adobe. Along the river-bottoms it is largely alluvial; in some places siliceous and micaceous.

Agriculture. The recent development of agriculture through irrigation has been the wonder of western civilization. In 1910 there were 46,170 farms, average value $10,645. The average number of acres per farm was 293, which was more than twice the size of the average farm in the United States. This is due to the number of stock-grazing-farms. Farm-products are cereals, roots, vegetables, fruit, hay-fodder, live stock, wool, dairying, poultry, honey, etc.

Colorado excels other states in the average value per acre of farm-crops. Owing to the superior quality of Colorado fruit, it is very extensively shipped to other states.

Mining. Colorado leads in the production of the precious and allied metals, producing twice as much gold and silver as any other state and more than one third of the total output of the United States. Colorado possesses inexhaustible coal-deposits, and in 1906 was seventh among the coal-producing states, surpassed by Pennsylvania, Illinois, West Virginia, Ohio, Alabama and Indiana in the order named. It ranked second among the states as a producer of anthracite, being surpassed by Pennsylvania. The Colorado coal-fields are found on both sides of the Rocky Mountains, those on the western slope being the largest and most important in quantity and quality. In the year 1910 the state produced 11,973,736 tons, which were valued at $17,026,934, and employed 15,864 men in and about the mines. Coke is manufactured extensively, the state ranking sixth in the amount of coke produced.

Manufacturing. The great variety of raw materials gives Colorado advantages as a manufacturing state. The leading manufacturing industries are the iron and steel plant at Pueblo, foundries and machine-shops at Denver, smelting of gold, silver, copper, lead and other ores, canning-factories, creameries and cheese-factories, flouring and grist-mills, printing and publishing plants, saw-mills, beet-sugar factories, etc. 