Page:Herschel - A Preliminary Discourse on the Study of Natural Philosophy (1831).djvu/104

 motion of material bodies and its cause, such as, What will happen when a moving body is surrounded on all sides by others not in motion? What will happen when a body not in motion is advanced upon by a moving one? It is evident that the answers to such questions as these can be no other than laws of motion, in the sense we have above attributed to laws of nature, viz. a statement in words of what will happen in such and such proposed general contingencies. Lastly, we are led, by pursuing the analysis, and considering the phenomenon of the aggregation of the parts of material bodies, and the way in which they influence each other, to two other general phenomena, viz., the cohesion and elasticity of matter; and these we have no means of analysing further, and must, therefore, regard them (till we see reasons to the contrary) as ultimate phenomena, and referable to the direct action of causes, viz. an attractive and a repulsive force.

(81.) Of force, as counterbalanced by opposing force, we have, as already said, an internal consciousness; and though it may seem strange to us that matter should be capable of exerting on matter the same kind of effort, which, judging alone from this consciousness, we might be led to regard as a mental one; yet we cannot refuse the direct evidence of our senses, which shows us that when we keep a spring stretched with one hand, we feel our effort opposed exactly in the same way as if we had ourselves opposed it with the other hand, or as it would be by that of another person. The enquiry, therefore, into the aggre-