30O THE LIMITS OF SCIENCE. . 



be produced, till we get to the violet and ultra violet, or actinic 

 rays, represented by revolutions at the rate of over 750 billions 

 per second. All these ether waves, set up by the revolutions of 

 the electrons, travel at (the same well-known rate— that of 186 

 thousand miles a second. But these waves are not matter at all. 

 Waves, unless accompanied by other forces, merely give a certain 

 motion to matter, and then leave it where it was. There is, how- 

 ever, another realm, besides that of tangible matter, which we 

 must investigate. Waves of heat and light are conveyed, not 

 only through our atmosphere, but through space, and the medium 

 by which they are conveyed we call the ether, and it not only fills 

 the whole of space, but also penetrates the whole of matter. 

 Although so far as I know, there is not any definite evidence to 

 show that ether is actually the ultimate material — if we may 

 call it material — of which the rest of matter is composed, the fact 

 of its extreme tenuity, as evidenced by its offering no apparent re- 

 sistance to the heavenly or any other bodies, and its universal 

 distribution, will, I think, compel us to rank it at any rate in the 

 first place among the " Probables " for the place of distinction, 

 and also oblige us to admit that we have now reached the limits of 

 science in this direction. 



III. What is the extent of the Universe? — One feels almost 

 overawed at the very idea of endeavouring to get an answer to 

 such a question. Only the distances of about forty stars have 

 been determined with anything like accuracy, and the nearest of 

 these, a Centauri, is so far that its light, travelling at 186,000 

 miles a second, takes about four years to reach us, whilst the 

 light of the very distant stars takes many thousand times longer. 

 Long after the discovery of the telescope it was found that the 

 greater the power of the instrument, the greater was the number 

 of stars to be discovered in the same area of the heavens, and 

 for a long time it appeared that this form of discovery would 

 go on indefinitely. It was only a matter of the power of the 

 telescope how many suns would be discovered, and telescopic 

 photography only at first seemed to lend its help to establish 

 the same theory, by showing more stars on the very sensitive 

 plate than could be seen on those less sensitive. But more recent 

 investigations seemed to show that a boundary of this infinite 

 source of discovery is being reached. The existence of vast num- 

 bers of dark stars, probably cooled down suns, is thought by some 

 to prevent our seeing more stars beyond, but clearly this objection 

 will not hold good, for, even if the dark stars exceeded the 

 number of light stars by 150,000 to one, the heavens would be as 

 bright as the face of the moon if the stars extended to infinity, 

 and it may be fairly concluded from this that they do not. 

 Authorities, however, seem to be very doubtful, generally, on 

 this point. So we must now admit having reached the limits of 

 science in this direction. 



IV. What is the extent of time? — How far can science take 

 up back in the past? and how far towards eternity in the future? 



