131 
THE PHARMACEUTICAL JOURNAL AND TRANSACTIONS. [September 7,18:2. 
is given in the speculations of Count Rumford about the 
physical properties of water, to which the President has 
already called your attention. Pure water attains its 
greatest density at a temperature of about 39^-° Fahr.; 
it expands and becomes lighter whether it is cooled or 
heated so as to alter that temperature. Hence it was 
concluded that water in this state must he at the bottom 
of the sea, and that by such means the sea was kept from 
freezing all through; as, it was supposed, must happen 
if the greatest density had been that of ice. Here then 
was a subtance whose properties were eminently adapted 
to secure an end essential to the maintenance of life upon 
the earth. In short, men came to the conclusion that 
the order of nature was reasonable in the sense that 
everything was adapted to some good end. Further 
consideration, however, has led men out of that conclu¬ 
sion in two different ways. First, it was seen that the 
facts of the case had been wrongly stated. Cases were 
found of wonderfully complicated structures that served 
no purpose at all; like the teeth of that whalebone whale 
of which you heard in section D the other day, or of the 
dugong, which has a horny palate covering them all up 
and used instead of them; like the eyes of the unborn 
mole, that are never used, though perfect as those of a 
mouse until the skull-opening closes up, cuttting them 
off from the brain, when they dry up and become inca¬ 
pable of use ; like the outsides of your own ears, which are 
absolutely of no use to you. And when human con¬ 
trivances were more advanced it became clear that the 
natural adaptations were subject to criticism. The eye 
regarded as an optical instrument of human manufac¬ 
ture, was thus described by Helmholtz; the physiologist 
who learned physics for the sake of his physiology, and 
mathematics for the sake of his physics, and is now in 
the first rank of all three. He said, “If an optician sent 
me that as an instrument, I should send it back to him 
with grave reproaches for the carelessness of his work, 
and demand the return of my money.” 
The extensions of the doctrine into physics were found 
to be still more at fault. That remarkable property of 
pure water, which was to have kept the sea from freez¬ 
ing, does not belong to salt water, of which the sea 
itself is composed. It was found, in fact, that the idea 
of a reasonable adaptation of means to ends, useful 
as it had been in its proper sphere, could yet not be 
called universal, or applied to the order of nature as a 
whole. 
Secondly, this idea has given way because it has been 
superseded by a higher and more general idea of what is 
reasonable, which has the advantage of being applicable 
to a large portion of physical phenomena besides. Both 
the adaptation and the non-adaptation which occur in 
organic structures have been explained. The scientific 
thought of Dr. Darwin, of Mr. Herbert Spencer, and of 
Mr. Wallace, has described that hitherto unknown pro¬ 
cess of adaptation as consisting of perfectly well-known 
and familiar processes. There are two kinds of these ; 
the direct process, in which the physical changes re¬ 
quired to produce a structure are worked out by the very 
actions for which that structure becomes adapted—as the 
backbone or notechord has been modified from genera¬ 
tion to generation by the bendings which it has under¬ 
gone ; and the indirect processes, included under the 
head of Natural Selection—the reproduction of children 
slightly different from their parents, and the survival of 
those which are best fitted to hold their own in the 
struggle for existence. If the naturalists here were able 
to talk to you for weeks, they might give you some idea 
of the rate at which we are getting explanations of the 
evolution of all parts of animals and plants, the growth 
of the skeletons, the nervous system and its mind, of leaf 
and flower. But what, then, do we mean by explanation? 
We were considering just now an explanation of a law T 
of gases ; the law according to which pressure increases 
in the same proportion in which volume diminishes. The 
explanation consisted in supposing that a gas is made up 
of a vast number of minute particles always flying 
about and striking against one another, and then showing 
that the rate of impact of such a crowd of particles on 
the sides of the vessel containing them would vary 
exactly as the pressure is found to vary. Suppose the 
vessel to have parallel sides, and that there is only one 
particle rushing backwards and forwards between them; 
then it is clear that, if we bring the sides together to 
half the distance, the particle will hit each of them 
twice as often, or the pressure will be doubled. Now it 
turns out that this would be just as true for millions of 
particles as for one, and when they are flying in all 
directions instead of only in one direction and its oppo¬ 
site ; provided only that they interfere with each other s 
motion. Observe now ; it is a perfectly well-known and 
familiar thing that a body should strike against an op¬ 
posing surface and bound off again; and it is a mere 
every-day occurrence that, what has only half so far to go 
should be back in half the time; but that pressure should 
be strictly proportional to density i3 a comparatively 
strange, unfamiliar phenomenon. The explanation de¬ 
scribes the unknown and unfamiliar as being made up of 
the known and the familiar, and this, it seems to me, is the 
true meaning of explanation. Here is another instance. 
If small pieces of camphor are dropped into water, they 
will begin to spin round and swim about in a most mar¬ 
vellous way. Mr. Tomlinson gave, I believe, the expla¬ 
nation of this. We must observe to begin with that 
every liquid has a skin which holds it; you can see that 
to be true in the case of a drop, wFich looks as if it were 
held in a bag. But the tension of this skin is greater in 
some liquids than in others; and it is greater in cam¬ 
phor and water than in pure water. When the cam¬ 
phor is dropped into water, it begins to dissolve and gets 
surrounded with camphor and water instead of water. 
If the fragment of camphor were exactly symmetrical, 
nothing more would happen; the tension would be 
greater in its immediate neighbourhood, but no motion 
would follow. The camphor, however, is irregular in 
shape ; it dissolves more on one side than the other; and 
consequently gets pulled about, because the tension of 
the skin is greater where the camphor is most dissolved. 
Now it is probable that this is not nearly so satisfactory 
an explanation to you as it w r as to me when I was first 
told of it, and for this reason. By that time I was 
already perfectly familiar with the notion of a skin upon 
the surface of liquids, and I had been taught by means 
of it to work out problems in capillarity. The explana¬ 
tion was therefore a description of the unknown pheno¬ 
menon wdiich I did not know how to deal with as made 
up of known phenomena which I did know how r to 
deal with. But to many of you possibly the liquid skin 
may seem quite as strange and unaccountable as the 
motion of camphor on water. And that brings me to 
consider the source of the pleasure we derive from an 
explanation. By known and familiar, I mean that which 
we know how to deal with, either by action in the ordi¬ 
nary sense, or by active thought. When, therefore, that 
which we do not know how to deal with, is described as 
made up of things that we do know how to deal with, 
we have that sense of increased power which is the basis 
of all higher pleasures. Of course, we may afterwards 
by association come to take pleasure in explanation for 
its own sake. Are we then to say that the observed 
order of events is reasonable, in the sense that all of it 
admits of explanation ? That a process may be capable 
of explanation, it must break up into similar constituents 
which are already familiar to us. Now, first, the process 
may itself be simple, and not break up; secondly, it 
may break up into elements which are as unfamiliar 
and impracticable as the original process. 
It is an explanation of the moon's motion to say that 
she is a falling body, only she is going so fast and is so 
far off that she falls quite round to the other side of the 
earth, instead of hitting it; and so goes on for ever. 
But it is no explanation to say that a body falls because 
