THE ANATOMY OF A STEEL RAIL 59 



simple instrument which has revealed so many wonders. 

 It enables the expert physician to tell the difference between 

 the blood of a human being and that of other animals ; the 

 mineralogist, to discriminate between very minute particles 

 of quartz or diamond ; the zoologist, to watch the embryonic 

 development of the starfish ; and it now permits the metal- 

 lurgist to study the anatomy of so apparently lifeless a 

 thing as a piece of steel. 



With a vertical illuminator, or kind of reflector which 

 takes the light rays from any source and bends them 

 through a right angle, and then permits the observer to 

 look through it down on to the polished surface of metal- 

 equipped with such a reflector attached to an ordinary 

 microscope, and with a number of different lenses called 

 objectives and eyepieces, the metallurgist can look at his 

 piece of rail under a linear magnification of forty to a 

 thousand diameters. This means that if a spot measuring 

 one hundredth of an inch across be magnified one hundred 

 diameters, the original spot would appear to the eye of the 

 observer one inch in diameter. 



Can you conceive of anything in that rail that could 

 escape the trained eye when under a magnification of one 

 thousand diameters? It would have to be more elusive 

 than the tiny germs which medical men look for as the 

 cause of most of our contagious diseases, than the 500,000 

 bacteria in a cubic centimeter of the ordinary milk we 

 drink. 



By throwing the structure which we see under the 

 microscope upon a ground glass in a special camera, and 

 then substituting a photographic plate for the ground glass, 

 a picture can be obtained in the usual way of photography. 

 Such a portrait of our rail may be seen in Fig. 1, which is 

 a fair average sample of a good steel rail. 



By examining this picture a little more closely, we notice 

 light and dark areas; the former are the pure iron grains, 

 or ferrite, as the metallurgist calls them, and the latter 

 "pearlite," because it looked like mother-of-pearl to the 



