“Physical science treats of matter, and what I shall to-night term its affections; namely, attraction, motion, heat, light, electricity, magnetism, chemical-affinity. When these re-act upon matter, they constitute forces. The present tendency of theory seems to lead to the opinion that all these affections are resolvable into one, namely, motion: however, should the theories on these subjects be ultimately so effectually generalized as to become laws, they cannot avoid the necessity for retaining different names for these different affections; or, as they would then be called, different modes of motion.”

“Each force is definitely and equivalently convertible into any other and that where experiment does not give the full equivalent, it is because the initial force has been dissipated, not lost, by conversion into other unrecognized forces. The equivalent is the limit never practically reached.”