748 
heat as a consequenee of its own contrac- 
tion, torn by conflicting currents and fiery 
eruptions, shrouded in absorbing vapors or 
perhaps in vast masses of flame, appeals at 
once to the popular imagination. Both 
branches of astronomy share in the advan- 
tages which follow this awakening of pop- 
ular interest ; for that popular interest in 
any science is to be deprecated is to my 
mind utterly inadmissible. The cultiva- 
tion of a pure science is possible only in 
those communities where such an intelli- 
gent interest exists. Without it we should 
not be here to-day. It is splendidly mani- 
fest around us. The only possible danger 
to be feared is that interest in results 
whose significance is readily understood 
may lead to an undervaluation by the pub- 
lic of results which are of the highest im- 
portance, but which only the trained spe- 
cialist can fully comprehend ; and this dan- 
ger will be avoided if scientific men publicly 
express their own appreciation of results 
which belong to the latter class. 
Popular interest which is not of this 
character, but which has no purpose other 
than amusement, is less desirable. ‘It is 
the universal law,” says Macaulay, ‘‘ that 
whatever pursuit, whatever doctrine, be- 
comes fashionable, shall lose a portion of 
that dignity which it had possessed while it 
was confined to a small but earnest minority, 
and was loved for its own sake alone.” 
Macaulay is here referring to a temporary 
interest in scientific matters which prevailed 
among fashionable circles in the reign of 
Charles the Second—to what would now be 
called a ‘fad.’ In our own time science 
occasionally suffers in much the same way. 
It is to be regretted that the habitability of 
the planets, a subject of which astronomers 
profess to know little, has been chosen asa 
theme for exploitation by the romancer, to 
whom the step from habitability to inhab- 
itants is a very short one. The result of 
his ingenuity is that fact and fancy become 
SCIENCE. 
[N.S. Vou. VI. No. 151. 
inextricably tangled in the mind of the ay 
man, who learns to regard communication 
with the inhabitants of Mars as a subject 
deserving serious consideration (for which 
he may even wish to give money to scien- 
tific societies), and who does not know that 
it is condemned as a vagary by the very 
men whose labors have excited the imagina- 
tion of the novelist. When he is made to 
understand the true state of our knowledge 
of these subjects he is much disappointed, 
and feels a certain resentment towards sci- 
ence, as if it had imposed upon him. 
Science is not responsible for these 
erroneous ideas, which, haying no solid 
basis, gradually die out and are forgotten. 
Thus it cannot long suffer from outside 
misapprehension, while the sustained effort 
necessary to real progress is in the end a 
sufficient safeguard against the intrusion of 
triflers into its workshops. 
In astrophysics sustained effort is as nec- 
essary as it is in other branches of science. 
There is an impression in some quarters 
that the results of astrophysical investiga- 
tion are easily obtained. That this is in 
some cases true may readily be admitted. 
I cannot regard it as areproach. It is one 
of the advantages to which I have referred 
by bringing new methods to bear on old 
problems. What an effort to grasp some- 
thing tangible we observe in the earlier 
writing on Fermat’s principle! What a 
groping in the dark after a principle felt 
rather than seen! and how obvious the 
same principle is from the point of view of 
the wave theory! In a field so wide and so 
little explored as astrophysics there must be 
novelties which can be gathered with com- 
paratively little effort, and which may 
nevertheless be of no small importance. 
But there are also problems whose solution 
calls for the exercise of the highest intel- 
lectual faculties, and for the most strenuous 
exertion. 
In astrophysics difficulties are met with 
