One peculiarity of this age is the sudden acquisition of much physical knowledge. There is scarcely a department of science or art which is the same, or at all the same, as it was fifty years ago. A new world of inventions—of railways and of telegraphs— has grown up around us which we cannot help seeing; a new world of ideas is in the air and affects us, though we do not see it. A full estimate of these effects would require a great book, and I am sure I could not write it; but I think I may.
