THE CONCEPTION OF THE GREAT REALITY. 



235 



secoudly, by employing an artificial retina a thousand times 

 more sensitive than the human. Now the human retina 

 receives the impression of what it looks at in a fraction of a 

 second, provided, of course, that the eye is properly focussed, 

 and no further impression will be made by keeping the eye 

 fixed on that object. But in celestial photography, when the 

 telescope is turned into a camera, the sensitive plate having 

 received the impression in the first second may be exposed not 

 only for many seconds or minutes or hours, but for an aggregate 

 of even days by re-exposure, every second of which time details 

 on tliat plate new objects sunk so far in the vast depths of space 

 as to be immeasurably beyond the power of the human eye, 

 even through telescopes hundreds of times more powerful than 

 tiie largest instruments that science has enabled us to construct, 

 and yet here is laid before us a faithful chart, by means of 

 which we may once more continue our journey through space. 

 A short exposure will show us firmaments and nebulai just 

 outside the range of our greatest telescopes, and every 

 additional second extends our vision by such vast increases 

 of distance that the brain reels at the thought; and yet, 

 as we have seen, exposures of these sensitive plates may be 

 made not only for seconds, but for thousands and even hundreds 

 of thousands of seconds ! And still there is no end, no end 

 where the weary mind can rest and contemplate ; the mind of 

 man can only cry out that there is no limit. In spite of all its 

 strivings and groping by aid of speculative philosophy, the 

 finite cannot attain to infinity, nor get any nearer to where 

 the mighty sea of time breaks in noiseless waves on the dim 

 shores of eternity. 



Let us now examine in a similar manner the second great 

 mystery, the Infinity of Time. 



With this object in view we will first consider the human 

 sense of sight and hearing, and take sound, or the vibrations 

 which affect the drutn of the human ear. Sound travels in air 

 at about 1,130 feet per second, and if the vibrating body giving 

 out the sound oscillates sixteen times in one second, it follows 

 that, spread over this 1,130 feet, there will be sixteen waves, 

 giving a length of about 70 feet to each wave. This is the 

 lowest sound that the human ear can appreciate as a musical 

 note. When the number of vibrations in a second sinks below 

 sixteen, the ear no longer appreciates them as a musical sound, 

 but hears them as separate vibrations or beats. The best 

 instrument for illustrating this is the " Syren." This comprises 

 a disc with sixteen holes pierced at regular intervals round the 



