BUNSEN AND KIRCHHOFF 333 



'spectroscopic double stars,' which even through the best 

 telescopes can only be seen as single stars, since they are 

 much too far away. But the regularly recurring doubling of 

 the spectral lines of these stars tells us that, and how quickly, 

 one of the two suns revolving about their common centre of 

 gravity approaches us, while the other recedes; and from this 

 we are able to calculate the orbit and in many cases even the 

 masses of these double suns in a logically consistent manner. 

 An important direct confirmation of the validity of Doppler's 

 principle for light has finally resulted from the observation of 

 earthly sources of light (glowing atoms in the canal rays) 

 moving at extremely high speeds. 



Spectrum analysis with all that has been built upon it, by 

 no means forms the only remarkable achievement of Bunsen 

 and Kirchhoff. 



Regarding Kirchhoff, we may mention his laws concerning 

 the flow of electric current in networks, and in conductors of 

 two-dimensional or solid form; these being enlargements of 

 Ohm's law. Bunsen further advanced science by a large 

 number of other researches which can only be mentioned 

 here in part, but concerned almost all directions of investi- 

 gation, and everywhere pointed out new roads and provided 

 new methods of attack. Everything that he undertook was 

 given new shape by him, and at the same time generally 

 became of practical importance. Thus he discovered, con- 

 tinuing Davy's electrolytic researches, the 'Bunsen element'^ 

 which then remained for a quarter of a century the only 

 existing useful source of strong electric current. 



By its use he then found the best method for the electro- 

 lytic preparation of pure metals such as calcium, aluminium, 

 magnesium; all of these became of technical importance 

 later. Burning magnesium, and also Davy's arc light fed 



^ This contains zinc in dilute sulphuric acid, and gas retort carbon in 

 concentrated nitric acid, and dates from the year 1841; later (1875) 

 Bunsen also suggested the chromic acid cell, which is likewise much used. 



