226 
POPULAR SCIENCE REVIEW. 
de la Fondation Lalande has this year been carried off by Mr. De la Rue for 
his labours in astronomical photography. 
To come to our summary of astronomical progress, proprement dit, we find 
Mr. Huggins again fortunate. Not content with having taught us the real 
constitution of nebulae, he has now thrown new light on the constitution of 
comets. Upon examining Comet I., 1866, wj^ich appeared in his telescope 
as an oval nebulous mass, surrounding a small and dim nucleus, the prism 
showed that the nucleus was self-luminous, that it consisted of matter in 
the state of ignited gas, and that this matter is similar in constitution to 
the gaseous material of some of the nebulae. The coma was found to shine 
by light derived from another source. Since the extremely diffuse matter 
of the coma cannot be supposed to contain solid or liquid matter at the high 
temperature necessary for incandescence, it seems almost certain that the 
coma reflects the sun’s light. On this supposition, the prism gives no infor- 
mation whether the material of the coma is solid, liquid, or gaseous. Ter- 
restrial phenomena suggest a condition similar to fog or cloud. If the luminous 
gas of the nucleus suffers condensation and subsequent diffusion to form the 
tails of comets, it must pass through a condition in which it neither emits 
nor in any large degree reflects light. Dark spaces are frequently seen 
between the envelopes of comets. 
Biela’s comet, on the other hand, has escaped us altogether, and we have 
thus been deprived of an opportunity of observing a phenomenon unique in 
astronomy, — that of a twin comet. Otto Struve’s and Mr. De la Rue’s sweeps 
have been altogether unavailing, and Mr. Talmadge thinks he glimpsed it once 
only in Mr. Barclay’s ten-inch refractor ; we may imagine, therefore, that it has 
been playing other pranks besides the one recorded. Before we part company 
with comets, we may mention that Faye’s comet, which, by the way, was 
mistaken by Father Secchi for Biela’s, has been well followed by Axel 
M oiler, who has communicated new elements of it to the Astronomische 
Nachrichten. Secchi’s places given in the Bulletino Meteorologico are of 
value. 
The Comptes Bendus have recently contained some papers by MM. Faye 
and Delaunay of the highest interest. Of M. Faye’s paper on the sun we 
shall delay a detailed account until our next writing. In the interim, we 
may remark that the first part of it contains the following conclusions deduced 
from Mr. Carrington’s researches 
1. Sun-spots are depressions beneath the surface of the sun’s photosphere, 
varying in depth from about to of the sun’s radius, i.e., from about 
40,000 to 20,000 miles. 
2. Many apparent irregularities in the proper motions of sun-spots hitherto 
supposed to be capricious, or attributable to cyclones or tornadoes, or to their 
own mutual actions, are now probably explicable by the continued variation 
in the motion proper to each successive parallel of the photosphere. 
3. The astonishing regularity in the motions of sun-spots, the maintenance 
of which is thus demonstrated by M. Faye, appears to that astronomer in- 
compatible with any hypothesis of mere superficial or local movements in 
the photosphere, but seems to point to some more general action arising from 
the internal mass of the sun. 
We may also mention that Professor Spoerer, of Anclam, in a memoir pre- 
