186 CORRELATION OF PHYSICAL FORCES. 



much embarrassed me in enunciating the propositions put 

 forth in these pages, on account of the imperfection of scien- 

 tific language ; an imperfection in great measure unavoidable, 

 it is true, but not the less embarrassing. Thus, the words 

 light, heat, electricity, and magnetism, are constantly used in 

 two senses viz. that of the force producing, or the subject- 

 ive idea of force or power, and of the effect produced, or the 

 objective phenomenon. The word motion, indeed, is only 

 applied to the effect, and not to the force, and the term chem- 

 ical affinity is generally applied to the force, and not to the 

 effect ; but the other four terms are, for want of a distinct 

 terminology, applied indiscriminately to both. 



I may have occasionally used the same word at one time 

 in a subjective, at another in an objective sense ; all I can 

 say is, that this cannot be avoided without a neology, which 

 I have not the presumption to introduce, or the authority to 

 enforce. Again, the use of the term forces in the plural 

 might be objected to by those who do not attach to the term 

 force the notion of a specific agency, but of one universal 

 power associated with matter, of which its various phenom- 

 ena are but diversely modified effects. 



Whether the imponderable agents, viewed as force, and 

 not as matter, ought to be regarded as distinct forces or as 

 distinct modes of force, is probably not very material, for, as 

 far as I am aware, the same result would follow either view ; 

 I have therefore used the terms indiscriminately, as either 

 happened to be the more expressive for the occasion. 



Throughout this essay I have placed motion in the same 

 category as the other affections of matter. The course of 

 reasoning adopted in it, however, appears to me to lead inev- 

 itably to the conclusion that these affections of matter are 

 themselves modes of motion ; that, as in the case of friction, 

 the gross or palpable motion, which is arrested by the con- 

 tact of another body, is subdivided into molecular motions or 

 vibrations, which vibrations are heat or electricity, as the 



