16 MAGNIFYING POWER OF LENSES. 



In order to explain the power of lenses in 

 magnifying objects and bringing them near us or 

 rather, in giving magnified images of objects, and 

 bringing the images near us we must examine the 

 different circumstances under which the same object 

 appears when placed at different distances from the 

 eye. If an eye placed at E looks at a man c b, fig. 2, 

 placed at a distance, his general outline only will be 

 seen, and neither his age, nor his features, nor his 

 dress will be recognised. When he is brought 

 gradually nearer us, we discover the separate parts of 

 his dress, till at the distance of a few feet we per- 

 ceive his features ; and when brought still nearer, 

 we can count his very eyelashes, and observe the 

 minutest lines upon his skin. At the distance E b, 

 the man is seen under the angle b E c ; and at the 



distance E B he is seen under the greater angle 

 BE A or bEA',; and his apparent magnitudes, cb, 

 A'b, are measured in those different positions by 

 the angles b E c, B E A, or b E A'. The apparent 

 magnitude of the smallest object may therefore be 

 equal to the apparent magnitude of the greatest. 

 The head of a pin, for example, may be brought 

 so near the eye that it will appear to cover a whole 



