the different steps in an
ordinary process of reasoning, if you will only take the trouble to
analyse it carefully. All the operations I have described, you will
see, are involved in the mind of any man of sense in leading him to
a conclusion as to the course he should take in order to make good a
robbery and punish the offender. I say that you are led, in that case,
to your conclusion by exactly the same train of reasoning as that which
a man of science pursues when he is endeavouring to discover the origin
and laws of the most occult phenomena. The process is, and always must
be, the same; and precisely the same mode of reasoning was employed by
Newton and Laplace in their endeavours to discover and define the causes
of the movements of the heavenly bodies, as you, with your own common
sense, would employ to detect a burglar. The only difference is, that
the nature of the inquiry being more abstruse, every step has to be most
carefully watched, so that there may not be a single crack or flaw in
your hypothesis. A flaw or crack in many of the hypotheses of daily life
may be of little or no moment as affecting the general correctness of
the conclusions at which we may arrive; but, in a scientific inquiry,
a fallacy, great or small, is always of importance, and is sure to be
constantly productive of mischievous, if not fatal results.

Do not allow yourselves to be misled by the common notion that an
hypothesis is untrustworthy simply because it is an hypothesis. It is
often urged, in respect to some scientific conclusion, that, after
all, it is only an hypothesis. But what more have we to guide us in
nine-tenths of the most important 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