CHEMISTRY SINCE TIME OF DALTON 



dence of a totally different kind has contributed to the 

 same end, from a source that could hardly have been 

 imagined when the Proutian hypothesis was formu- 

 lated, through the tradition of a novel weapon to the 

 armamentarium of the chemist the spectroscope. 

 The perfection of this instrument, in the hands of two 

 German scientists, Gustav Robert Kirchhoff and Rob- 

 ert Wilhelm Bunsen, came about through the investi- 

 gation, towards the middle of the century, of the mean- 

 ing of the dark lines which had been observed in the 

 solar spectrum by Fraunhofer as early as 1815, and by 

 Wollaston a decade earlier. It was suspected by 

 Stokes and by Fox Talbot in England, but first brought 

 to demonstration by Kirchhoff and Bunsen, that these 

 lines, which were known to occupy definite positions in 

 the spectrum, are really indicative of particular ele- 

 mentary substances. By means of the spectroscope, 

 which is essentially a magnifying lens attached to a 

 prism of glass, it is possible to locate the lines with 

 great accuracy, and it was soon shown that here was a 

 new means of chemical analysis of the most exquisite 

 delicacy. It was found, for example, that the spectro- 

 scope could detect the presence of a quantity of sodium 

 so infinitesimal as the one two -hundred -thousandth 

 of a grain. But what was even more important, the 

 spectroscope put no limit upon the distance of location 

 of the substance it tested, provided only that sufficient 

 light came from it. The experiments it recorded might 

 be performed in the sun, or in the most distant stars or 

 nebulae; indeed, one of the earliest feats of the instru- 

 ment was to wrench from the sun the secret of his 

 chemical constitution. 



