ON MATTER, FORCE, AND MOTION IN SPACE. 49 



belong, a field large enough to expatiate in, even 

 without regard to its continuity with space and worlds 

 beyond. 



And first, as to space that great recipient and 

 container of all things which are the subject of human 

 sense, and, through the senses, of human science. 

 Putting aside the metaphysics of the Infinite, as thus 

 applied, and the old subtleties of the plenum and 

 vacuum controversy, the question presses upon us in 

 this form : ' What is contained in space, beyond, and 

 apart from, those aggregates of matter, great or small, 

 of which our senses and other means of observation 

 give us knowledge ? ' As early as the times of Em- 

 pedocles and Aristotle the question of the TO ^ra^v 

 some medium between the objects of sense and 

 the percipient being forced itself upon philosophy. 

 Modern science, dating here, as in so many other cases, 

 from the era of Newton, has given more definite form 

 to the enquiry ; and taking certain of the great powers 

 of nature as interpreters, has shown from these the 

 necessity of supposing a material medium as .the sole 

 conceivable means of their transmission through space. 



What there is of theory in this matter has been 

 well borne out by observation and experiment. The 

 interplanetary spaces of our own system, as the most 

 accessible and fruitful field of research, have been 

 zealously worked upon, with results which rank among 

 the most wonderful attainments of science. Light, 

 heat, and gravitation, those great elemental forces or 

 powers, in the relations they establish between the sun 

 and the earth, first gave a scientific character to the 



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