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.

ON THE PHYSICAL BASIS OF LIFE [92]

In order to make the title of this discourse generally intelligible, I have translated the term “Protoplasm,” which is the scientific name of the substance of which I am about to speak, by the words “the physical basis of life.”  I suppose that, to many, the idea that there is such a thing as a physical basis, or matter, of life may be novel—­so widely spread is the conception of life as a something which works through matter, but is independent of it; and even those who are aware that matter and life are inseparably connected, may not be prepared for the conclusion plainly suggested by the phrase, “The physical basis or matter of life,” that there is some one kind of matter which is common to all living beings, and that their endless diversities are bound together by a physical, as well as an ideal, unity.  In fact, when first apprehended, such a doctrine as this appears almost shocking to common sense.

What, truly, can seem to be more obviously different from one another, in faculty, in form, and in substance, than the various kinds of living beings?  What community of faculty can there be between the bright-coloured lichen, which so nearly resembles a mere mineral incrustation of the bare rock on which it grows, and the painter, to whom it is instinct with beauty, or the botanist, whom it feeds with knowledge?