Science progress* 



No. 28. 



June, 1896. 



Vol. V. 



THE GROWTH OF OUR KNOWLEDGE OF 



HELIUM. 



THE DISCOVERY OF THE LINE D 3 , 1868. 



IN the year 1868, spectrum analysis was first utilised in 

 endeavouring" to unravel the message which was con- 

 veyed to us by a most interesting eclipse observed in India. 

 The diagrams will indicate the kind of record with which 

 we have to deal in studying these celestial hieroglyphics. 

 We are in one part dealing with the long waves of light, 

 the red ; we are in the other dealing with the shorter waves 

 of light, the blue. The work done in that eclipse is 

 indicated by the bright lines — the hieroglyphics — which, 

 when translated as they have been, describe for us the 

 chemical nature of the particular stuff in the sun, which 

 made him put on a blood-red appearance " on his getting 

 out of his eclipse ". Taking the notes in the light scale 

 which are lettered in the ordinary spectrum of sunlight, in 

 order that they may be easily recognised and remembered, 

 we learn the particular qualities of the light emitted by the 

 blood-red streak. 



We have one quality represented by the line D, another 

 at C, and another at F. According to the diagram, one of 

 the lines is in the position of D. One observer said it was 

 "at D, or near D ". 



Soon after this eclipse was observed in India, a method, 



18 



