CLASSIFICATION OF THE CLOUDS. 659 



Cumulus, Cumulo- stratus, and Nivibus* With regard to form oi 

 appearance, they may also be divided into two classes, both occurring at 

 all altitudes, viz., fibrous or linear, which tend to arrange themselves in 

 layers, lines, or streaks ; and massive or compact, which take the form of 

 heaps or piles. f 



Clouds are seen at all levels between the highest Cirrus and the lowest 

 Stratum, so that it is often difficult to determine whether a particular sheet 

 or layer of Cloud belongs to the upper or the lower system. In such 

 cases, the observer will be greatly assisted by remembering how the 

 Clouds have become formed, whether by the gradual subsidence of the 

 highest forms, or by the ascent of the lower Clouds. 



The naming of Clouds is a most difficult subject for observers, and that 

 attended by mosij mistakes. The misnaming of certain Clouds is the 

 cause of most error : Cirro-cumulus and Cirro-stratus for example ; 

 Nimbus, too, no matter from what form of cloud rain falls it is called 

 Nimbus. It should be noted that Clouds of slight vertical depth, com- 

 pared with their area, belong to the Stratus types, while those that assume 

 solid and rounded masses are Cumulus forms. J 



In the Trade Wind region, by observing the direction of the upper 

 Clouds, it would appear that an opinion may be formed of the probable 

 direction of the squalls in unsettled weather, as previously remarked by 

 Captain Toynbee (pages 260—261). 



The Upper Clouds are considered on good authority to be composed 

 of particles of ice, inasmuch as the phenomena of halos, &c., are produced 

 by them, and these can only be explained by the refraction of the rays of 

 light through ice-crystals. 



Cirrus is often seen after a continuance of fine light weather, as a fine 

 whitish line of cloud, stretched across the sky at a great height, the ends 

 seeming lost in the horizon. This is often the first indication of a change 

 to wet weather ; to this line of Cirrus others are added laterally, and at 

 times clouds of the same sort seem to proceed from the sides of the line, 

 and are sent off in an oblique or transverse direction, so that the whole 

 may have the appearance of net- work. The line alluded to above is called 



• In abbreviating these names the following system has been used by the Meteoro- 

 logical OfliGe, as others have been found to mislead : — Cir. ; Cir. c. ; Cir. s. ; Str. ; 

 Gum. ; Cum. s. ; Nim. Another system, now in use, is C. for Cirrus; S. for Stratus ; 

 K. for Cumulus ; and N. for Nimbus. The amount of cloud is registered from " Blue 

 sky" to 10 "Entirely overcast." 



f These classes cannot always be separated when the Clouds are near the zenith, 

 and only their under-surfaces are seen ; viewed laterally they are easily distinguished. 

 It is important, however, to notice that the thread-like appearance of those Clouds, 

 whose vertical diameter as compared with the horizontal is small, is always partially, 

 and often wholly, due to perspective. Whether partially or wholly so, we can at once 

 decide, by looking at the same kind of Cloud in different azimuth ; e.ff., the bands of 

 Cirrus are real, since they appear to converge in opposite points of the horizon ; streaks 

 of Stratus are mostly phenomenal only, since looked at all round the vault of the sky at 

 the same distance from the zenith, they are commonly seen as lying in the same 

 Apparent plane. 



+ " Notes on taking Observations on Board Ship," by Capt. D. W. Barker, R.N.R. 

 ir the " Quarterly Journal of the Royal Meteorological Society," vol. xiil 1887, 

 page 187. 



