-1859] WRITINGS OF JOSEPH HENRY. 91 



but in liis mind it did not take that definite character which 

 it has since assumed under the influence of inductive science. 

 It was with him the vague and indefinite product of the 

 imagination, unconditioned by the actual phenomena of Na- 

 ture. It was adopted by Newton, who employed it with much 

 success in the different branches of his investigations; but in 

 modern times it owes its greatest development and range of 

 application, to Dr. John Dalton, of Manchester, England, and 

 still later principally to Mr. James Joule and Professor Wil- 

 liam Thomson. By means of it we are enabled to present in 

 a single line a series of facts which could not otherwise be ex- 

 pressed in many pages, and also to exhibit to the mind the 

 connection of a series of phenomena which could not, without 

 this aid, be definitely conceived. It is intimately connected 

 with all branches of physical science, and (strange as it may 

 appear) particularly with agriculture ; and we may therefore 

 be excused for presenting it in its broadest applications, and 

 with considerable detail. 



According to this theory every portion of the whole uni- 

 verse, or at least that part of it which is accessible to us by 

 means of the telescope, is occupied by atoms inconceivably 

 minute, hard, and unchangeable, definitely separated from 

 each other by attraction and repulsion. This assemblage 

 of atoms constitutes the substance of the material universe; 

 and to their attractions and repulsions, the forces by which 

 they are actuated, is referable all the power or energy which 

 produces the changes to which matter is subjected. 



These atoms, thus endowed, form a plenum throughout all 

 space, constituting what is called the setherial medium, and 

 in it, at wide intervals from each other, are isolated masses 

 of grosser matter, which constitute our world, the planets, 

 the sun, and stars. These also consist of atoms of another 

 order, or of groups of atoms, with spaces between them, wide 

 in comparison with the size of the atoms, which spaces are 

 pervaded by the minuter atoms of the setherial medium. 

 These bodies move in the medium without encountering 

 any sensible resistance. 



The various isolated bodies of the universe act upon each 



