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imagined spaces between the imagined molecules, just as particles 

 of sugar when dissolved are distributed throughout a vessel of 

 water. It is the medium whereby light and heat are conveyed 

 from the sun to the earth, and from the lamp on our table to the 

 book we are reading. It forms a boundless, shoreless sea, in and 

 throughout which worlds, systems, and universes are scattered hke 

 islands and archipelagoes in an infinite ocean. Without it there 

 would be eternal darkness and an utter absence of heat. It is an 

 unquiet sea too, one that is never at rest, an ocean that knows no 

 calm. It is in a continual tremor, and billions on billions of infi- 

 nitesimal waves are rolling across and athwart it every instant of 

 time, and in every possible direction. But it is invisible, and com- 

 pletely defies positive detection. It does not appear to be subject 

 to gravitation, as all other kinds of matter are ; and it is non- 

 molecular, as no other kind of matter is. It is a pure invention, 

 totally and completely unlike any form of matter with which man 

 is acquainted, and one which he has been obhged to endow with 

 opposing properties. There is not the slightest direct proof of its 

 existence ; like other theories this depends for proof on the Balance 

 of Probabilities, — the identical kind of proof, notice, by which we 

 establish the existence of a Creator. Yet no scientific man doubts 

 the fact of its existence, neither must we, if we have any hope of 

 understanding the laws of light, heat, electricity, and magnetism. 

 " Of its reality," says Tyndall, " most scientific men are as con- 

 vinced as they are of the existence of an atmosphere." And I can- 

 not see how we are to escape believing in it ; at all events it is quite 

 impossible to explain natural phenomena satisfactorily without 

 assuming its existence. It was imagined at first to be totally dis- 

 tinct from matter ; that it had no weight, and offered not even an 

 infinitesimal resistance to any object moving through it. It was 

 opposed by some on the ground that the heavenly bodies moving 

 in it must to some extent, however small, be retarded in their 

 motions ; and that if so, each planet must gradually approach its 

 sun, and finally fall into it. If the Ether revolved with the planets 

 this need not happen, but we cannot entertain this supposition from 

 the fact that the planets move with different velocities. If we sup- 

 pose the Ether to pass through the bodies among the molecules, as 

 water passes through the meshes of a net, there must still needs be 

 friction. The keen mathematical mind of Sir William Thompson 

 has come to the conclusion that the Ether does offer some resist- 

 ance, and tnat it does possess weight. He calculates that one 

 thousand million cubic miles of it may weigh one pound. 



In some of its properties as before mentioned it is opposed to the 

 ordinary laws of matter, and especially in connection with its power 

 of wave transmission. The wave-transmitting power of any sub- 



