10 THE PROGRESS AND SPIRIT OF 



difficult and abstruse in proportion as we generalise and 

 reduce them to their simplest terms. With respect to force, 

 more especially the most eminent philosophers of our time, 

 while declining any metaphysical definition, have been con- 

 strained to adopt new methods of regarding and describing 

 it, in those various actions upon or through matter which 

 testify to its presence and energy. Centres of force (an ex- 

 pression due to Boscovich in its scientific use), lines of force, 

 polar force, &c., are terms found necessary to express the 

 several modes of force in action, irrespectively of all questions 

 as to its abstract nature, or especial relations to matter. 

 Under the gradual adoption of this new language, there has 

 been a corresponding abandonment of phrases, more hypo- 

 thetical in themselves, and far less fitted to aid the progress 

 of scientific enquiry. As such we may denote that expression, 

 current even in some of our best systematic works, of the 

 f imponderable substances or forms of matter ; ' which, as de- 

 scribing heat, light, and electricity, makes assumptions wholly 

 unproved; and in excluding gravitation, chemical, mechanical 

 and vital forces from the same category, affirms a distinction 

 which we do not absolutely know to exist. For the notion of 

 an imponderable element (if notion it can be called) that of 

 a mode of change, or motion of matter, might probably in 

 all these cases be more truly as well as advantageously sub- 

 stituted. Such phrase better defines the present limit of our 

 knowledge, and marks a possible path of progress beyond. 

 Science, it may fairly be said, is constantly tending to 

 a closer form of logic in these matters ; and simple induc- 

 tion from facts, unfettered by names and prior notions, is 

 here as elsewhere the best guide to all ulterior discovery. 



The great problem respecting force in the most general 

 conception of it as a motive power on matter, is involved in 

 the question, whether it can ever really be lost or extin- 

 guished, or even lessened? or whether the,seeming cessation 



