ant affairs of daily life than hypotheses,
and often very ill-based ones? So that in science, where the evidence of
an hypothesis is subjected to the most rigid examination, we may rightly
pursue the same course. You may have hypotheses and hypotheses. A man
may say, if he likes, that the moon is made of green cheese: that is an
hypothesis. But another man, who has devoted a great deal of time and
attention to the subject, and availed himself of the most powerful
telescopes and the results of the observations of others, declares that
in his opinion it is probably composed of materials very similar to
those of which our own earth is made up: and that is also only an
hypothesis. But I need not tell you that there is an enormous difference
in the value of the two hypotheses. That one which is based on sound
scientific knowledge is sure to have a corresponding value; and that
which is a mere hasty random guess is likely to have but little value.
Every great step in our progress in discovering causes has been made
in exactly the same way as that which I have detailed to you. A person
observing the occurrence of certain facts and phenomena asks, naturally
enough, what process, what kind of operation known to occur in nature
applied to the particular case, will unravel and explain the mystery?
Hence you have the scientific hypothesis; and its value will be
proportionate to the care and completeness with which its basis had been
tested and verified. It is in these matters as in the commonest affairs
of practical life: the guess of the fool will be folly, while the guess
of the wise man will contain wisdom. In all cases, you see that the
value of the result depends on the patience and faithfulness with
which the investigator applies to his hypothesis every possible kind of
verification.

I dare say I may have to return to this point by-and-by; but having
dealt thus far with our logical methods, I must now turn to something
which, perhaps, you may consider more interesting, or, at any rate,
more tangible. But in reality there are but few things that can be more
important for you to understand than the mental processes and the means
by which we obtain scientific conclusions and theories.* ([Footnote]
*Those who wish to study fully the doctrines of which I have endeavoured
to give some rough and ready illustrations, must read Mr. John Stuart
Mill's 'System of Logic'.) Having granted that the inquiry is a proper
one, and having dete