"O, my dear Kepler!" writes Galileo to his friend, "how I wish that we could have one hearty laugh together! Here at Padua is the principal Professor of Philosophy, whom I have repeatedly and urgently requested to look at the moon and planets through my glass, which he pertinaciously refuses to do. Why are you not here? What shouts of laughter we should have at this glorious folly! And to hear the Professor of Philosophy at Pisa lecturing before the Grand Duke with logical arguments, as if with magical incantations to charm the new planets out of the sky!" Rub a stick of wax against your coat-sleeve, and it emits sparks: hold it near to light, fleecy particles of wool or cotton, and it first attracts, then it repels them. What do you understand about that, Mr. Pettipo, except merely that it is so? Stroke the cat's back before the fire, and you will observe the same phenomena. Your own body will, in like manner, emit sparks in certain states, but you know nothing about why it is so. Pour a solution of muriate of lime into one of sulphate of potash--both clear fluids; but no sooner are they mixed together than they become nearly solid. How is that? You tell me that an ingredient of the one solution combines with an ingredient of the other, and an insoluble sulphate of lime is produced. Well! you tell me a fact; but you do not account for it by saying that the lime has a greater attraction for the sulphuric acid than the potash has: you do not _understand_ how it is--you merely see that it is so. You must believe it. But when you come to Life, and its wonderful manifestations, you are more in the dark than ever. You understand less about this than you do even of dead matter. Take an ordinary every-day fact: you drop two seeds, whose component parts are the same, into the same soil. They grow up so close together that their roots mingle and their stalks intertwine. The one plant produces a long slender leaf, the other a short flat leaf--the one brings forth a beautiful flower, the other an ugly scruff--the one sheds abroad a delicious fragrance, the other is entirely inodorous. The hemlock, the wheatstalk, and the rose-tree, out of the same chemical ingredients contained in the soil, educe, the one deadly poison, the other wholesome food, the third a bright consummate flower. Can you tell me, Mr. Pettipo, how is this? Do you understand the secret by which the roots of these plants accomplish so much more than all your science can do, and so infinitely excel the most skillful combinations of the philosopher? You can only recognize the fact--but you can not unravel the mystery. Your saying that it is the "nature" of the plants, does not in the slightest degree clear up the difficulty. You can not get at the ultimate fact--only the proximate one is seen by you.