BESSEMER STEEL. 299 



is no longer tenable, for we really do know the composition of 

 the stars. 



The Spectroscope not only tells us the substance of which the 

 sun and the most distant stars are made, but gives us the same 

 information about the " gay motes that people the sunbeam." 

 It tells us that they are common salt in very minute particles. 

 They have been dashed into the air by the winds as spray, and 

 then dispersed over the whole globe. This is one reason why 

 we have so much salt in our bodies, and why the blood and 

 the tears are so salt. 



It is also applied to the arts. The well-known Bessemer 

 process consists in pouring melted iron into a peculiarly shaped 

 vessel called a " converter, " and blowing air through it for 

 the purpose of burning out the carbon. From the mouth of 

 the converter issues a volume of magnificent flames, and at a 

 certain moment the skilled workman who directs the process 

 inverts the vessel and pours out the steel. A very few seconds 

 too soon or too late would spoil the whole of the metal, in the 

 former case it being simply brittle cast-iron ; and, in the second, 

 becoming so thick that it could not be poured out. 



Only a few workmen could judge rightly the exact point 

 at which to shut off the air-blast. They watched the flame, 

 and by some change in it, too slight to be noticed by any 

 except experienced eyes, knew the moment when the iron was 

 converted into steel. 



Such men could, of course, demand any wages they liked, 

 and, by striking, stop the whole works. The Spectroscope, 

 however, performed this delicate discrimination far better than 

 the best workman. When directed to the flame, the bright 

 lines indicating carbon are seen in the spectrum. When the 

 blast has continued for some twenty minutes, the carbon lines 

 suddenly disappear, showing that the carbon has been burned 

 out, and giving to the workman the signal to shut off the air- 

 blast. 



Another discovery was, that liquids gave dark lines, 

 technically termed absorption bands, of different widths and in 

 different parts of the spectrum. Even liquids which had no 

 perceptible colour threw bands as bold as those which were 



