234 



SYDNEY T. KLEIN, F.L.S., F.R.A.S., ON 



rays falling on its surface into a bright point of light behind 

 it ; now place such a lens between your eye and a star, taking 

 a star so far away that the eye unaided can only just see it as 

 a glimmer of light, what happens ? Why, instead of the eye 

 receiving only a faint and almost imperceptible quantity of 

 light, it appears now to take in the whole mass of rays which 

 pass through the larger lens ; for the lens has caused them to 

 converge into a pencil of light sufficiently minute to enter the 

 eye ; thus the eye receives as much light as though the pupil 

 had been enlarged to the dimensions of the lens. Thus armed, 

 to what remoteness may we not now reach ? The star might 

 now be withdrawn so deep into space that the whole light 

 concentrated by the lens is not more intense than the faint 

 ray was from the star in its first position ; and this mighty 

 acquisition has been attained by the simple interposition of a 

 piece of glass, and of coarse the larger the lens the further we 

 can pierce into space. We now come back to the second part 

 of our question : — " Why does an object become apparently 

 smaller and smaller as it is withdrawn from the eye, until 

 it at last disappears from sight ? " The reason is, that the eye 

 is a very imperfect instrument for viewing objects at a great 

 distance ; the eye can only see an object when it is near 

 enough to subtend a certain angle, or in popular language, 

 to show itself a certain size, in fact, the eye cannot single 

 out and appreciate parallel rays. Could it do this, objects 

 would not grow smaller as they are removed. This pencil 

 might be removed to the moon, 240,000 miles away, and 

 would still appear to the eye the same size as it does 

 here close to you, but the result would be inconvenient. You 

 would never be able to see at one and the same time anything 

 larger than the pupil of your eye. The beauties of the land- 

 scape would be gone, and our dearest friends would pass us 

 unheeded and unseen ; everyday life would resolve itself into a 

 task similar to that of attempting to read our newspaper every 

 morning by means of a powerful microscope ; we should 

 commence by getting on to a big black blotch, and, after 

 wandering about for half an hour, we might then begin to find 

 out that we were looking at the little letter e, but anything 

 like reading would be quite out of the question. We may, 

 therefore, be thankful that our eyes have the imperfection of 

 not appreciating parallel rays. But we will now consider how 

 this imperfection may be remedied by science. There are two 

 ways of doing this, viz., firstly, by increasing the amount of 

 light received, by means of telescopes of great aperture ; and 



