For an easy, popular view of the principle of scientific idealism, perhaps nothing has been better said than by Thomas Carlyle, in his review of Novalis. "To a transcendentalist [says Carlyle] matter has an existence, but only as a phenomenon. Were _we_ not there, neither would _it_ be there: it is a mere relation, or rather the result of a relation between our living souls and the great First Cause; and depends for its apparent qualities on our bodily and mental organs; having itself no intrinsic qualities; being, in the common sense of the word, nothing. The tree is green and hard, not of its own natural virtue, but simply because my eye and my hand are fashioned so as to discern such and such appearances under such and such conditions. Nay, as an idealist might say, even on the most popular grounds, _must_ it not be so? Bring a sentient being with eyes a little different, fingers ten times harder than mine, and to him that thing which I call tree shall be yellow and soft, as truly as to me it is green and hard. Form the nervous structure in all points the reverse of mine, and this same tree shall not be combustible and heat-producing, but dissoluble and cold-producing; not high and convex, but deep and concave; shall simply have _all_ properties exactly the reverse of those attributed to it. There is no tree there; but only a manifestation of power from something which is not _I_. The same is true of material nature at large, of the whole visible universe, with all its movements, figures, accidents and qualities." Scientific idealism, as far as we have gone with it, has now become one of the "_exact_" sciences--as much so as physics. It has been simply the result of continuous and innumerable experiments in natural philosophy, for three centuries. There is no need of going into these physical particulars, after they have been put into the school-books of children and explained in popular lectures. One more quotation must suffice. Mr. G. H. Lewes, in his _Biographical History of Philosophy_, tells us that