ory only when the facts themselves
support it. Once planted victoriously on the conquered ramparts the
hypothesis becomes a theory--a generalization of science--marking a
fresh coign of vantage, which can never be successfully assailed unless
by a new host of antagonistic facts. Such generalizations, with the
events leading directly up to them, have chiefly occupied our attention.

But a moment's reflection makes it clear that the battle of science,
thus considered, is ever shifting ground and never ended. Thus at
any given period there are many unsettled skirmishes under way; many
hypotheses are yet only struggling towards the stronghold of theory,
perhaps never to attain it; in many directions the hosts of antagonistic
facts seem so evenly matched that the hazard of war appears uncertain;
or, again, so few facts are available that as yet no attack worthy the
name is possible. Such unsettled controversies as these have, for the
most part, been ignored in our survey of the field. But it would not be
fair to conclude our story without adverting to them, at least in brief;
for some of them have to do with the most comprehensive and important
questions with which science deals, and the aggregate number of facts
involved in these unfinished battles is often great, even though as yet
the marshalling has not led to final victory for any faction. In some
cases, doubtless, the right hypothesis is actually in the field, but its
supremacy not yet conclusively proved--perhaps not to be proved for many
years or decades to come. Some of the chief scientific results of the
nineteenth century have been but the gaining of supremacy for hypotheses
that were mere forlorn hopes, looked on with general contempt, if at
all heeded, when the eighteenth century came to a close--witness the
doctrines of the great age of the earth, of the immateriality of heat,
of the undulatory character of light, of chemical atomicity, of
organic evolution. Contrariwise, the opposite ideas to all of these
had seemingly a safe supremacy until the new facts drove them from the
field. Who shall say, then, what forlorn hope of to-day's science may
not be the conquering host of to-morrow? All that one dare attempt is
to cite the pretensions of a few hypotheses that are struggling over the
still contested ground.

SOLAR AND TELLURIC PROBLEMS

Our sun being only a minor atom of the stellar pebble, solar problems
in general are of course stellar problems also. But