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imagined spaces between the imagined molecules, just as particles 
of sugar when dissolved are distributed throughout a vessel of 
water. Itis 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 like 
islands and archipelagoes in an infinite ocean. Without it there 
would be eternal darkness and an utter absence of heat. Itis 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 imfi- 
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 a/l 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 obliged 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 itis 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 Etherrevolved 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 Wiluam Thompson 
has come to the conclusion that the Ether does offer some resist- 
ance, and taat 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- 
