THE LAW OF CONTINUITY. 31 



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 elec- 

 tricity, 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 trans- 

 mutation by processes of motion too unstable to be caught and de- 

 tained 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 an- 

 other 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-esti- 

 mating 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 per- 

 manence has hitherto unduly infiuenced 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 scru- 

 tiny of the majority of the acutest investigators of Nature who have 

 lived. 



The noble generalization of the conservation of energy affords an- 

 other 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. 



