desert of the gardens. How much better to-day is the world for their energy, their strenuousness and their power? Are we any more lovable or stronger or wiser?
I have sometimes amused myself wondering what question I would ask an inhabitant of Mars, if communication with that planet could be established. If but one question could be answered, what should that question be? Is there any one question which everybody would be willing to have asked and forego every other one? Would it be a question of astronomy or of biology or of philosophy? Each one should settle for himself what that question ought to be, if its answer was to be of interest to all mankind. If it were of a religious or philosophical kind, think what happiness or misery would befall the most of us when the answer came. It would be almost like a judgment day and half the world or more would be thrown into a suicide mood. Ignoring momentous questions, what others are we really most concerned to have answered? Do we not all want to know of the nature of life, of mind, and of all the activities of nature displayed in phenomena? Does not everybody ask, 'What is electricity?' 'What is life?' I do not remember ever to have heard the question 'What is gravitation?' though it is certainly one of the most obscure of all the great activities of nature. Not a particle of matter escapes its hold, and the law of inverse squares we have all learned so glibly, we take on the basis of uniform experience. How can such action be the outcome of inherent properties of matter, and what must be the texture and distribution in the ether so compelling?
Surmises by the score have been made, but none are satisfied with any attempt to find a reason or the antecedents of the phenomenon. It conditions every phenomenon of every kind that comes to our knowledge in a gravitative way, but hitherto it has quite eluded the most ingenious of guessers, and most persons who have been concerned with its problems have either abandoned attempts at its solution or have unwarrantably concluded it is insoluble. There is no good reason why it should be thought of as an ultimate problem, and its solution belongs to the twentieth century or some of its successors. In my judgment its rationale will be found some time.
When, a hundred years ago, men said that heat was caloric, it is plain on a little thinking that such an answer brought us no nearer the real solution. Giving the thing a new name was not an explanation. We have been taught for a generation that heat is a mode of motion, and when we now think of the phenomena we think of brisk changes of position of the minute particles of a body, and that idea reveals heat as a condition of matter, not a thing in itself any more than the spin of a top is to be thought of as a thing to be described apart from the top.
A hundred years ago light was thought to be a kind of corpuscle
