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POPULAR SCIENCE REVIEW. 
into clouds ; in attaining to a greater height ; and lastly, in 
being seen all round the sun’s limb, whereas the jets are 
limited to the neighbourhood of the spots . 
Pl um es are sometimes simple, sometimes compound. Some 
forms of simple plumes are presented in figs. 5 and 6 (Plate 
LXXXI. ). Amongst other forms, Secchi notes plumes terminated 
by diffuse clouds, or crossed by two or three sets of clouds, or 
doubled down upon themselves, or attached to a cloud by a 
tail. (Most of these forms have been already described and 
illustrated.) Near the poles, “ evidently on account of the 
absence of directing currents, they take an almost vertical 
form, with a diffused cloudy summit as in fig. 6.” Compound 
jets form appearances not readily classified. Some are reti- 
culated as in fig. 7, an arrangement due to the interlacing of 
distinct plumes. “ Thus, in fig. 8, the masses of streamers 
diverging from three centres join and form arcades, through 
which appear black spaces. When these streamers are more 
numerous and extended, they appear as in fig. 9, where the 
crossing of the threads in all directions produces cornered inter- 
stices.” But where the crossing streamers are diffused the 
interstices assume an oval or rounded appearance, as in fig. 10. 
“ These masses attain the enormous heights of from 150 to 240 
seconds. Their summits are generally very much broken up, 
and strongly resemble the masses of cirro-cumuli which we see 
at the borders of rain clouds. One fact with regard to them is 
very interesting ; it is, that however distinctly marked and well 
defined the separation of the streamers may be at their base, 
after a certain height they become completely mingled with 
each other, and form a mass which appears to be quite uniform 
in structure.” 
Secchi gives some interesting particulars respecting solar 
clouds, — as he terms those masses which float above the chroma- 
tosphere, fig. 11, Plate LXXXI. “One class of clouds,” he 
remarks, “is produced by the breaking up of plumes ; others 
appear to be plumes which have ceased to be fed by the chroma- 
tosphere, and therefore become detached. The very curious phe- 
nomenon is sometimes presented of a cloud suddenly forming 
itself into plumes (figs. 12 and 13), showing that these plumes 
can take their origin from gaseous matter, and do not require an 
orifice of projection for their formation. M. Tacchini, of 
Palermo, has also made this observation, and we have both seen 
the jet directed downwards like a fiery rain.” 
Secchi’s remarks upon the physical distinction between 
plumes and jets, as well as upon the association between pro- 
minences and the phenomena of the sun’s surface, are of extreme 
interest and importance. “ In distinguishing between jets and 
plumes,” he says, “ I have no intention to decide as to whether 
