SCIENTIFIC SUMMARY. 
317 
pressure, possibly in internal temperature, and even in the cohesion and 
fusibility of materials ; for though there is certainly every probability in 
favour of the assumption that the earth and her companion are identical as 
to composition, it cannot be considered as absolutely demonstrated, or per- 
haps demonstrable. The supposition that the same elementary forms prevail 
throughout the solar system has been rendered indefensible by spectroscopic 
enquiry. Not to insist on minor planetary differences, which as yet may be 
uncertain in their indication, unsolved mysteries yet hang around the central 
region of light and fire, and the two outermost planets ; of which, prior to 
the introduction of spectrum-analysis, the telescope could give no kind of 
information. However, in dealing with selenological enquiries, we can 
make no other assumption but that of identity with terrestrial materials ; 
and we should only be justified in abandoning it by difficulties on that 
hypothesis insuperable. 
Whatever may be the theories of modern geologists, or whatever changes 
may yet await some of their conclusions, one thing seems evident, that the 
eruptive force which has moulded the surface of the moon into its present 
strange configuration has been decaying down to either comparative or 
absolute extinction. It is certainly not very material whether our genera- 
tion may be contemporary with its expiring efforts, or with a subsequent 
state of quiescence ; but it is a question not without much interest ; and few 
observers would not hail with pleasure an opportunity of witnessing the 
activity of a lunar volcano. However, it is still mbjudice whether anything 
of the kind has occurred since the invention of the telescope ; and there is- 
more difficulty than might be supposed in forming a reliable opinion, partly 
from the inaccuracies and mistakes of the earlier observers, partly from the- 
deficiencies of existing maps, and partly from the backwardness to supply 
those deficiencies at the hands of the possessors of the powerful instruments 
of the day. Close investigation and careful drawing is required, and that 
under several angles of illumination ; and though photography may render 
most important service, as that of an eye which never omits anything, yet 
the circumstances would be very exceptional which would give to its ren- 
derings the keenness and certainty of ocular inspection. Each mode may 
help the other. It is of course among the minutest craters, and, according* 
to that great authority Schmidt, among the fissures or cracks, that we must 
seek for the evidence of remaining chemical life. But change of perhaps a 
less intelligible nature may be detected among the multitude of light-streaks 
and brilliant patches which variegate the fully-enlightened moon with such 
perplexing intricacy. There is strong evidence of altered brightness in 
some places, and it is much to be wished that some careful, patient observer 
would undertake the task of giving us a portion at least of a map of the full 
moon. 
Mars . — The next opposition of this planet in 1877 will, it is believed, 
give a very reliable value of the solar parallax ; and the Astronomer Royal 
has prepared a chart of stars suitable for comparative observation. 
The Minor Planets . — In the “Berliner Astron. Jahrbuch ” for 1878 
Professor Tietjen has published the approximate places of 144 of the 160 
small planets for the present year, and accurate opposition ephemerides 
of 71. — Flora. From corresponding observations of this body in 1873, 41 
