A great deal has been done in mechanical invention and chemical discovery. In these respects the world has moved immensely since the beginning of the present century. It is the habit of some short-sighted people to predict that we have, as a race, arrived at the pinnacle of our greatness, so far as relates to the subjugation of the brute forces of nature We have, say they, now harnessed the forces of gravity, heat, electricity, light, and affinity, we have learned how far it is possible to make them work for man, and henceforth, whatever improvement is to be made, must be only in the form of the harness. It is the habit of this class of men to not only regard the steam engine as capable of improvement only in trivial details, in variations in the form of cut-off, or other subordinate particulars, but to look upon electricity as a necessarily more expensive force to generate than heat, and as consequently, forever debarred from economic use as a generator of motive power for machinery. They consider the application of light as limited to the various kinds of photography now known, and which may hereafter be developed. They discern no remote possibility in the enormous force of chemical affinity, although it is through one of the commonest manifestations of that force—combustion—that we get the heat for our engines, dwellings, dyehouses, furnaces, and forges. Although the present era in science has given to the world [the great doctrine of the mutual convertibility of these forces, and the cognate and equally important doctrine of the conservation of force, the possibilities which a consideration of these doctrines open to the mind, do not seem to force themselves upon their understandings. " To give a glimpse of some of these possibilities is the object of the present article. When we, divesting our minds of all preconceptions, examine our relations to the things which surround us, we find all these relations resolving themselves into motion. It is primarily through motion that we get any knowledge of anything, and practically it is motion which feeds,clothes, and warms us. Growth is motion. The changes which take place in the substances which we take as food, is a movement of their molecules and their rearrangement in the tissues of our bodies, where they rest not day nor night until finally eliminated and thrown out as effete matter. Nor even then do they rest. There is no rest in nature. Motion is life : nay, more ; it and matter together constitute the whole category of physical existence. It follows that whatever force can contribute to the physical and mental welfare or the pleasures of mankind—and it is in this only that invention finds a profitable field—must be i capable of being converted into mass motion; for the human control of molecular motion depends upon mass motion. J To illustrate this let us consider the growth and preparation of any article of food, as wheat. It is by the mass motion of the plow and the harrow the ground is prepared to receive the seed; in this way the molecular motions concerned in its growth are aided, and the full ear and plump berry obtained. It is by mass motion that it is harvested, thrashed, ground, and kneaded, preparatory to the molecular changes which take place in its conversion into bread. It is by mass motion that it is masticated and mixed with the saliva in the mouth, to facilitate the molecular change it must undergo in the process of digestion. As in this, so in all chemical processes, mass motion is employed to control the molecular motion, and this mass motion is, to a very great extent, in the present age of the world, communicated through the agency of machinery. But we also find that the mass motion pf machines is obtained by the aggregation of molecular motions, so that in a ceaseless cycle these forms of motion flow one into the other The chief field for inventors must, then, continue to he in the future as it has been in the past, in the employment of machines as intermediate'links between molecular motion and other molecular or mass motion, which it is desired to make minister to the wants of mankind. If we now accept the modern view that light, electricity, and gravity are, as well as heat, but modes of molecular motion, who shall dare to say that machinery may not be made the connecting link between them and other modes of molecular motion, in the future, as successfully as it is now between heat and work. It sounds odd to speak of a light engine, or a gravity engine, although we are familiar enough with caloric engines, steam engines, and electric engines; and a water wheel is but a gravity engine, although we know that previous to the action of gravity it was, so to speak, " wound up" by the action of heat upon the water of the sea. There is yet an almost unlimited field for lesser lights in the invention of improvements on present forms and devices, but the geniuses of the future have more glorious work before them. When the vast coal-fields upon which the world at present relies shall have been consumed, there will be just as much carbon as before, only it will exist in another form. The mass motion which it will have produced in assuming that form, will in its turn have been converted into molecular motions of some kind, which will be capable of re-conversion without loss into mass motion again, and the world's great workshop will keep running—no fear about it. Where, then, shall invention stop ? When man ceases to want anything to minister to body or mind, then will invention cease. What is there left to do? So much, which is possible, that the ages to come will never see it all accomplished.