452 METEOROLOGY. 



locomotivof while objects more removed, beyond the second plane, move 

 in the same direction. We cannot caution observers too much aiiamst 

 this error, especially when there are three or four strata of super^josed 

 clouds, some having the same direction, and others opposite ones. 



Very often, also, the cirri are so slow that it must take many hours 

 to comprehend their march. This extreme slowness contributes to a 

 lateral movement perpendicular to their advance still more i)ronouuccd 

 than tiiat of the cumulus or other types of clouds ; to this must be 

 added their filamentous form and the great number of their ramifications. 

 In this case the observer must take a bench-mark upon some elevated 

 structure in the city or the summit of a mountain or top of a tree, verify- 

 ing it from hour to hour, and if these precautions are not yet sufiicient, 

 wait until the cirrus has passed the meridian or disappeared at the op- 

 posite horizon. Generally, at the observatory at Havana, the direction 

 of cirrus is definitely noted upon the register only in the afternoon, 

 although it has appeared at five or six o'clock in the morning. 



When a cumulus is swelling up from a base below the horizon toward 

 the zenith it presents the appearance of a motion which must be dis- 

 tinguished from the true direction of the cloud. 



Cirrus, cirro-stratus, and cirro-cumulus come generally from the south- 

 west, showing presence of the superior equatorial current. 



Cumulus, cumulo-stratus, and fracto-cumulus, on the contrary, appear 

 toward the northeast, determining the inferior polar current. But the 

 cumuli from June to December generally take a middle direction, from 

 the east, under the influence of the northeast and southeast trade- winds, 

 while the fracto-cumulus accompanies the polar current from the north- 

 east, from December to May, when this last, going against the current 

 from southeast of the southern hemisphere, draws near the equator and 

 causes the trade-winds to descend from north to east-northeaf?t, or east. 



Moreover, the i^a/Zio-cirn^-'? and the pall io-cumulus serve alternately as 

 a transition between these two opposite currents, the equatorial and jjolar, 

 although the first type accompanies more frequently the superior cur- 

 rent and the second the inferior current; so that these two pallia 

 alternate in the.following order : 



Cirrus, ^ 



■Cirro-stratus, /• Superior equatorial current. 

 Cirro-cumulus. J 

 Pallio-cirrus. 

 Pallio-cumulus. 



Cumuhis. ? Inferior polar current. 



Fracto-cumulus, ) 



TELOCITY OF CLOUDS. 



Our present uncertainty as to the velocity of clouds, the difficulties 

 which are presented to a single observer, perhaps, deprived of sufficient 

 knowledge or suitable instruments to undertake directly this calculation, 



