With regard to the changes in the general conditions of society and the advance in human knowledge, think for one moment what fifty years have done! I have often imagined myself escorting some wise man of the past to our Saturday Club, where we often have distinguished strangers as our guests. Suppose there sat by me, I will not say Sir Isaac Newton, for he has been too long away from us, but that other great man, whom Professor Tyndall names as next to him in intellectual stature, as he passes along the line of master minds of his country, from the days of Newton to our own,--Dr. Thomas Young, who died in 1829. Would he or I be the listener, if we were side by side? However humble I might feel in such a presence, I should be so clad in the grandeur of the new discoveries, inventions, ideas, I had to impart to him that I should seem to myself like the ambassador of an Emperor. I should tell him of the ocean steamers, the railroads that spread themselves like cobwebs over the civilized and half-civilized portions of the earth, the telegraph and the telephone, the photograph and the spectroscope. I should hand him a paper with the morning news from London to read by the electric light, I should startle him with a friction match, I should amaze him with the incredible truths about anesthesia, I should astonish him with the later conclusions of geology, I should dazzle him by the fully developed law of the correlation of forces, I should delight him with the cell-doctrine, I should confound him with the revolutionary apocalypse of Darwinism. All this change in the aspects, position, beliefs, of humanity since the time of Dr. Young's death, the date of my own graduation from college! I ought to consider myself highly favored to have lived through such a half century. But it seems to me that in walking the streets of London and Paris I shall revert to my student days, and appear to myself like a relic of a former generation. Those who have been born into the inheritance of the new civilization feel very differently about it from those who have lived their way into it. To the young and those approaching middle age all these innovations in life and thought are as natural, as much a matter of course, as the air they breathe; they form a part of the inner framework of their intelligence, about which their mental life is organized. To men and women of more than threescore and ten they are external accretions, like the shell of a mollusk, the jointed plates of an articulate. This must be remembered in reading anything written by those who knew the century in its teens; it is not likely to be forgotten, for the fact betrays itself in all the writer's thoughts and expressions.