Essay on Motion and Force. 



273 



others maintain, " ordinary matter," and yet so attenuated 

 as to manifest in an " indefinitely small degree, the most 

 ordinary properties of matter," and the dense parts are 

 in a great degree the conveyors of these undulations, it 

 follows, that as the density of this medium must vary 

 greatly in different parts of the interplanetary regions, 

 all calculations of distance, founded upon astronomical 

 observations, depending upon the transmission of light 

 through so unequally dense a medium, must be liable to 

 error ; and it is scarcely possible, that this would not have 

 been discovered, during the long series of observations 

 which have been made by observers who would not be 

 likely to overlook any source of inaccuracy. 



The theory of an imponderable, all-permeating, and 

 equally dense medium is a hypothesis, reaching beyond 

 matter, and as such is not properly a subject for physical 

 investigation. It is only an attempt to answer, that, to 

 human understanding, unanswerable question, why matter 

 moves. 



What appears to be the main argument against the 

 theory of a medium composed of ordinary matter in an 

 attenuated condition, is, that no medium is required for 

 transmission of motion though molecular intervals. Other- 

 wise we suppose that in certain states of matter the ulti- 

 mate particles actually touch each other, and that matter 

 in this peculiar condition actually touches other matter, 

 which the known law of attraction seems to refute. If 

 this reasoning is not faulty, and the fact be admitted that 

 motion can be transmitted through small intervals, there 

 certainly can be no difficulty in supposing the same to be 

 the case through larger intervals, and analogy would cer- 

 tainly lead us to that belief. 



Finally, I fail to see why it is better philosophy to assume 

 intermediate force between motion and the " First Cause," 

 of all things, than to suppose no force between matter and 

 that cause ; or why it is better to suppose one force than 

 many. It is, I think, an unnecessary hypothesis leading to 



