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CLOVER

4X3

COAL

never seen below the summit of Mt. Blanc,

which is nearly 16,000 feet in elevation.

2.   Cumulus clouds are those which look like  great  mountains of  cotton piled  one on top of another and resting on a horizontal base. It is highly probable that the rounded top of these  clouds  results  from columns of hot, moist air rising and thrusting their tops into the upper and hence cooler regions of the atmosphere.

3.   Stratus  clouds  consist   of  large   flat layers or horizontal sheets. They are seen very frequently about sunset.

4.   The nimbus or rain cloud has no particular  form,   but   generally  is  large  and gray or dark.

Regarding the causes which operate to produce clouds, we may group them all tinder one general head, namely, a lowering of the temperature of the air below the dew-point. Among the particular causes which produce this fall of temperature are the following:

(a) Radiation of heat from the earth to space, especially at night. This is the most frequent cause of fogs on land, (b) Radiation from the earth's atmosphere to space, (c) Expansion of heated air on rising to higher regions of the earth's atmosphere where the pressure is less, (d) A cold wind blowing into a region filled with warm, moist air.

Another condition necessary for the formation of clouds is the presence in the air of small dust-particles or of ions. This fact has been demonstrated mathematically by Kelvin and experimentally by Aiken. In reply to the frequent query as to why the clouds do not fall, it is to be said, first, that they may be falling when in quiet air, but, secondly, when particles are as small as those involved in the case of clouds, their surface becomes enormously large compared with their mass; so that the resistance which the air offers to a falling body of this size is also enormous when compared with its weight. Hence the rate of fall is, in general, so minute as to escape observation.

Clo'ver, species of the genus Trifolium, belonging to the pea family, The name is chiefly applied to those species which are used in agriculture. It is also sometimes applied to species of other genera in the same family, as the sweet clover, which is Melilotus; prairie clover, which is Peta-lostemon, etc. About 300 species of Tri-folium have been described, and they are well-known by their habit and three-f oliolate leaves. The common red clover (T. pra-tense) is probaHy not native to North America, but has come from Europe. The white clover (T. repens) has been introduced from Europe, but is also probably native to North America. Numerous native species belong to North America, especially in the far west.

Cloves. See SPICES.

Clo'vis, king of the Franks, was born 465 A D., and died in 511. He conquered the Gallo-Romans, and overran the whole country between the Somme and the Loire. His wife, Clotilda, was a Christian, and earnestly wished her husband to become a Christian also. In a great battle with the Alemanni Clovis was hard pressed, and at last in despair cried to the God of Clotilda, offering to become a Christian if he got the victory. The Alemanni were driven from the field and on Christmas day Clovis and his soldiers were baptized; while he received from the pope the title of Most Christian King.

Clyde, the most important river of Scotland. It flows for 106 miles, past Lanark, Bothwell and Glasgow, the head of navigation, and at Dumbarton becomes a firth. Near Lanark are the four famous Clyde falls. Below Glasgow large sums have been spent in deepening the channel, so that the former depth of 15 inches at low water has now become from 18 to 20 feet. The first steamboat in Europe was launched on the Clyde in 1812. The last 14 miles of the river, together with the firth, which slowly widens from one to 37 miles, are one of the world's chief commercial waterways. There is a very large amount of shipbuilding on the Clyde.

Clytemnestra. See AGAMEMNON.

Coal, a name applied to considerable aggregations of carbonaceous matter of vegetable origin. Coal has no definite chemical composition, the proportion of carbon varying from 95 per cent, or even more down to 70 per cent, or a little below. Coal occurs in beds interstratified with shale, sandstone, etc. The vegetation from which coal was made is believed to have grown where the coal now occurs. At the time of the growth of the vegetation, the regions where it grew are believed to have been swamps comparable, except in size, to the peat-bogs of the present time. As the vegetation growing in the bogs died, it fell into the water of the swamps, as in the case of the Dismal Swamp of the present time. Beneath the water the dead vegetation did not decay as it would have done in the open air, though it underwent chemical changes. The first series of changes resulted in its transformation into peat. After the accumulation of considerable beds of vegetable matter in the swamps, the sites of the swamps seem to have been submerged, probably by sinking. When submerged, either beneath the sea or beneath the waters of lakes,. sediment, such as sand or mud, was deposited over the accumulated vegetable matter. Thus buried, the vegetable matter was still more completely shut off from the air and underwent further chemical changes. At the same time the weight of the sediment above