464 PHYSICAL GEOGRAPHY. 



scheme is now universally adopted, which will be briefly given, placing Mr.. Foster's 

 English names beside the Latin nomenclature of the former writer. 



1. Cirrus Curlcloud. This form of cloud exhibits light, flexuous, or diverging fibres, 

 sometimes shooting out from a nucleus in all directions, resembling a lock of hair, or a 

 crest of feathers. The name refers to this feature of its external character. It occurs, 

 however, in parallel bars, or thread-like lines, spanning a vast extent of the atmosphere, 

 the whole breadth of the sky being insufficient to show the extremities. Other lines also 

 are occasionally presented, crossing these at right or oblique angles, as in a piece of net- 

 work. In the former condition we have linear cirrus, and in the latter reticular cirrus. 

 These are the cobwebs of the sky. They frequently appear stretching their white and 

 delicate fibres between the dark and dense masses, as if spun to connect them, though 

 really distinct and far separated. The cirri appear in the higher regions of the 

 atmosphere, and are the most elevated of the clouds. Viewed from the summits of high 

 mountains, while the traveller looks down upon other forms of cloud, he beholds these 

 still above him, and apparently at 'as great a distance as when seen from the plains. The 

 appearance of true cirrus, or curlcloud, is supposed to indicate variable weather ; when 

 most conspicuous and abundant, to presage high winds and rain ; and when the streaming 

 fibres have pointed in a particular direction for any length of time, the gale may be 

 expected to blow from that quarter. 



2. Cumulus Stackencloud. This modification of cloud occurs in the lower regions 

 of the atmosphere, and is easily recognised. It is commonly under the control of the sur- 

 face winds, and frequently exhibits a very magnificent appearance. It consists of a vast 

 hemispherical or conical heap of vapour rising gradually from an irregular horizontal base, 

 and increasing upwards. Hence the names, cumulus, a pile or heap, and Stackencloud, a 

 number of detached clouds stacked into one large and elevated fabric. Cumuli are the 

 accompaniments and prognostics of fine weather. They begin to form soon after sunrise, 

 from irregular and scattered specks of cloud, which then appear at a moderate elevation, and 

 are the nuclei of the ultimate formations. As the morning advances the nucleus enlarges, 

 or several coalesce, and early in the afternoon, when the temperature of the day is at its 

 maximum, the cumulus attains its greatest magnitude. The cloud decreases as the sun 

 declines, and is usually broken up towards sunset, rapidly separating into fragments, after 

 the manner of its construction. The cumulus may be called the cloud of day, from the 

 interval between morning and evening generally measuring the term of its existence. 

 Its appearance considerably varies in the detail, and often exhibits a brilliant silvery 

 light, and a copper tinge, when in opposition to the sun, indicating a highly electrical con- 

 dition of the atmosphere. 



3. Stratus Fallcloud. The former name, meaning a bed or covering, alludes to the 

 position occupied by this cloud, immediately contiguous to the surface of the earth ; and 

 the latter to its origin, by the subsidence of vapour in the atmosphere. Unlike the 

 cumulus, it eminently belongs to the night, appearing at eventide, reaching its maximum 

 density soon after midnight, and commonly vanishing with the opening morn. This 

 class of clouds comprehends all those fogs and creeping mists, which, in the calm evenings 

 of hot summer and autumnal days, appear spread like a mantle over the surface of the 

 valleys, plains, lakes, and rivers. The Roman poet held the nocturnal visits of the stratus 

 to the lower levels to be an indication of continued fair weather : 



" Then mists the hills forsake, and shroud the plain," 



a meteorological axiom, founded upon the popular experience, as true now as in the days ! 

 of Virgil. The dissipation of the stratus does not always take place with the opening 

 morn, no more than the wreck of the cumulus with the return of night, though in both 



