Let us suppose that in tracing its cycloidal curves through the unthinkable reaches of space traversed by the solar system our planet should pass through a "belt" of attenuated matter having the property of dementing us! It is a conception easily enough entertained. That space is full of malign conditions incontinuously distributed; that we are at one time traversing a zone comparatively innocuous and at another spinning through a region of infection; that away behind us in the wake of our swirling flight are fields of plague and pain still agitated by our passage through them,--all this is as good as known. It is almost as certain as it is that in our little annual circle round the sun are points at which we are stoned and brick-batted like a pig in a potato-patch--pelted with little nodules of meteoric metal flung like gravel, and bombarded with gigantic masses hurled by God knows what? What strange adventures await us in those yet untraveled regions toward which we speed?--into what malign conditions may we not at any time plunge?--to the strength and stress of what frightful environment may we not at last succumb? The subject lends itself readily enough to a jest, but I am not jesting: it is really altogether probable that our solar system, racing through space with inconceivable velocity, will one day enter a region charged with something deleterious to the human brain, minding us all mad-wise. By the way, dear reader, did you ever happen to consider the possibility that you are a lunatic, and perhaps confined in an asylum? It seems to you that you are not--that you go with freedom where you will, and use a sweet reasonableness in all your works and ways; but to many a lunatic it seems that he is Rameses II, or the Holkar of Indore. Many a plunging maniac, ironed to the floor of a cell, believes himself the Goddess of Liberty careering gaily through the Ten Commandments in a chariot of gold. Of your own sanity and identity you have no evidence that is any better than he has of his. More accurately, I have none of mine; for anything I know, you do not exist, nor any one of all the things with which I think myself familiarly conscious. All may be fictions of my disordered imagination. I really know of but one reason for doubting that I am an inmate of an asylum for the insane--namely, the probability that there is nowhere any such thing as an asylum for the insane.