Page:The American Cyclopædia (1879) Volume IV.djvu/725

 CLOUDS CLOVER 713 cloud ring. The burning rays of the sun are intercepted by it. The place for the absorption and reflection, and the delivery to the atmos- phere of the solar heat, is changed ; it is trans- ferred from the upper surface of the earth to the upper surface of the clouds." Clouds are thus not merely the gatherers and distributors of rain to all parts of the earth, but they are a curtain spread before the sun to intercept its fierce heat, and check at night the too rapid evaporation from the soil heated during the day by its rays. "Where they are not formed, and the surface is exposed to the sun, there we infer that water cannot be present, and the ground must be a parched desert. Such ap- pears to be the condition of the side of the moon presented to the earth, no clouds ever being seen to obscure its disk. It has been shown by Tyndall that invisible vapor also has the power of absorbing radiant heat, and thus, by intercepting the fierce rays of the sun du- ring the day, or the radiation of heat from the earth at night, of preventing, in atmospheres supplied with moisture, those great changes in temperature which take place in arid trop- ical regions. (See "Contributions to Molec- ular Physics in the Domain of Eadiant Heat," New York, 1873.) Little is known of the causes that produce the brilliant and varied colors often assumed by the sky, particularly at sunset. They are unquestionably, however, connected with the aqueous vapor contained in the atmosphere; and the reddish hue, the most common of all, is probably owing to the greater facility with which these rays are transmitted through the watery vesicles. Re- flected from the surface of distant hills, they even give to these a delicate roseate hue. The electricity of the clouds is a subject for more especial reference in the articles ELECTRICITY and LIGHTNING. Aqueous vapor being a better conductor of electricity than the dry air, the heavy clouds gather this force from the atmos- phere around, some strata being positively and some negatively electrified. When separated by comparatively dry atmosphere, these clouds, or the clouds and the earth, are in the condition of a Leyden jar, ready to be discharged with sudden report when the non-conductor which separates them is broken through. As the clouds thicken and the watery particles more nearly approach each other, the electricity contained in the whole cloud gathers upon its surface, and at last acquiring sufficient ten- sion to break through the non-conducting me- dium, the electrical equilibrium is establish- ed with the flash of lightning and the roar of thunder. The electrical condition of the clouds has been referred to as the cause of their being often gathered around the summits and sides of mountains, as if they were attracted to these, as light floating substances when electrified rush toward bodies in their vicinity. But the phenomena explained in the early part of this article show that the low temperature prevail- ing in these localities is sufficient to account for the continual formation of a cloud, causing it to appear permanent, when it is but a process of condensation of new vapors brought on by the winds replacing those which are swept away and rendered invisible, as they dissolve in the warmer airs at a distance. CLOUGH, Arthur Hngh, an English author, born in Liverpool, Jan. 1, 1819, died in Florence, Italy, Nov. 13, 1861. He was educated at Rugby school, and at Balliol and Oriel col- leges, Oxford. In 1842 he gained a fellowship at Oriel, which he resigned in 1848, because his theological opinions did not accord with those of the established church. In 1848-'9 he travelled on the continent. He was in Rome, where he was intimate with the leading Italian liberals, during the siege of that city by the French. Upon his return to England he was made principal of University hall, and pro- fessor of the English language and literature in University college, London. In 1852 he re- signed this appointment, came to America, settled at Cambridge, Mass., and engaged in teaching and literary pursuits. The next year he returned to England to accept a position under the committee on education. After the close of the Crimean war he was appointed secretary to a commission to examine the mili- tary systems of the continent. At the time of his death he was travelling for the benefit of his health. His chief work, a poem in hex- ameters entitled " The Bothie of Tober-na- Vuolich," was published in 1848. In 1858 the "Amours de Voyage," a story in verse, ap- peared in the " Atlantic Monthly." He revised Dryden's translation of " Plutarch's Lives " (Boston, 1859), and just before his death wrote " Mari Magno," a series of tales. A collection of his poems, with a memoir by Charles Eliot Norton, appeared in Boston in 1862. CLOVER (trifoUum), a genus of plants be- longing to the natural order leguminosce, com- prising 59 species, and generically distinguished as tufted or diffuse herbs, with flowers in heads or spikes, leaves mostly palmately trifoliate, a persistent 5-cleft calyx, the standard of the co- rolla longer than the wings, small 1-6-seeded pods, and stipules joined with the petioles. From the three leaflets which constitute its leaf it takes the name rptyv/l/lov in Greek, tri- folium in Latin, and trefoil in English. There are several of the many varieties of clover of great value to agriculturists. Red clover (T. pratense) is a biennial plant, having perennial qualities under special modes of cultivation, and is particularly adapted to argillaceous soils. Small clover, or the rowen crop, is excellent for young stock; but animals should not be permitted to feed on clover lands in early spring or late in the autumn ; in the latter case the crop is likely to be winter-killed for want of a mulch-like protection, and in the former is not able to regain full vigor during the after part of the season, and this is especially true if sheep are the pasturing stock. Land may be seeded down to clover with any of the cereal