62 POPULAR LECTURES AND ADDRESSES. 



contact with any side of the other, and allowed 

 to take the relative position to which it will 

 obviously tend that in which the bars perpen- 

 dicular to the common sides of the two cubes 

 come together end to end there will be produced, 

 by pure gravitation, a force of attraction between 

 them which may be of any amount, however 

 great, and which will be the greater the greater 

 the ratio of the whole space unoccupied within the 

 boundary of either cube, to the space occupied 

 by the matter of the bars. 



The illustration has been chosen merely for the 

 sake of definiteness and simplicity ; but it is clear 

 that any arrangement, however complex, of woven 

 fibrous structure, provided only the ratio of the 

 unoccupied to the occupied space is sufficiently 

 great, will lead to the same general conclusion. 

 Farther, it is clear that the same result would be 

 produced by any sufficiently intense heterogene- 

 ousness of structure whatever, provided only some 

 appreciable proportion of the whole mass is so 

 condensed in a continuous space in the interior 

 that it is possible, from any point of this space 

 as centre, to describe a spherical surface which 

 shall contain a very much greater amount of 

 matter than the proportion of the whole matter 

 of the body which would correspond to its volume. 

 Except in imposing this condition, the theory 

 now suggested interferes with no molecular hypo- 

 thesis hitherto propounded, continuous or atomic, 



