has also been adopted in the electro-chemical arrangement of metals. Upon the possibility of placing all bodies in a continuous list under the head of any property whatever—cohesion, elasticity, and so on—the opinion is now entertained that all matter is capable of receiving, holding, and giving forth, any kind of force.
The varieties of force themselves have been instructively reduced to a single basis—that of motion; electricity, gravity, light, and all the rest, are at present referred to the movement in particular orbits and planes of the ultimate particles which build up all masses. For any sort of force can be converted by suitable means into any other, and all into common mechanical motion. Now, as transformations of energy are incessant in Nature—changes whereby heat becomes electricity, electricity light, and light chemical action—it must be that there are intermediate phases which a body assumes while passing from the manifestation of one of these forces to another. It must be that the ordinary forms of force just named, which seem to be so broadly marked off from each other, must be really united in transmutation by processes of motion too unstable to be caught and detained by our comparatively rude methods of detection and arrest. The extremes of a series we see, the links between elude us.
The kinds of motion to which are given names in our works on physics are, perhaps, only the stable varieties of an indefinitely great number. The swiftness of the transitions from one stable form to another may explain and excuse the notion long held that the different kinds of force were individual entities, unrelated to each other.
Here one of the chief lessons taught us by the law of continuity comes in: we are confronted by a variety of seemingly isolated forces; we find them taking on indifferently one another's forms; and, although we know not how they do so, yet we can see the danger of over-estimating the apparent, while much more may be present though hidden from our sight. The comprehension of all the varieties of force under the one category of motion is hardly fraught with any deduction more suggestive than that which inclines us to acknowledge that mere permanence has hitherto unduly influenced our ideas of what the modes of motion may be in extent and diversity. The existence of electricity was unsuspected, except in the case of rubbed amber, until within a few generations; the fleeting character of the force evading the scrutiny of the majority of the acutest investigators of Nature who have lived.
The noble generalization of the conservation of energy affords another fact and hint of much value. It tells us of the radical identity of all sorts of force, whether as that of the descending clock-weight; or in a simple form of much fixity, as that of heat; or evanescent and easily convertible, as electricity; or intricate and with many paths of working, as chemical affinity; or beyond the reach of any but vague and general means of examination, as the forces of nerve and brain.