PRESIDENTIAL ADDRESS SECTION A. 33 



Wollaston (1802) and Fraunhofer (1814) made the next step 

 by producing a purer spectrum by means of a slit, througli which 

 they passed sunlight, and they found the spectral band was crossed 

 by numerous dark lines. 



Fraunhofer mapped these lines, which now bear his name, 

 and lettered the strongest of them A, B, C, D, etc., to K, but, 

 it was reserved for Kirchoff (1859) to explain the meaning of 

 them. 



Foucault in 1848 had indeed made the observation which is 

 at the foundation of modern spectroscopy when he showed that the 

 light from a powerful electric arc, when passed through a flame 

 tinted yellow by the volatisation of a sodium salt and examined 

 in a spectroscope, showed two black lines which were identical 

 in position with the D lines which Fraunhofer had found in the 

 sun. Sodium vapour absorbs just that particular light from a 

 hotter source which it emits in a cooler source of light. The same 

 is true of all other incandescent gases. 



The vapour of incandescent iron, examined in the spectro- 

 scope, shows a very large number of emission or bright lines, and 

 if this spectrum is placed alongside a solar spectrum it is seen 

 that everv line has a dark counterpart in the sun's spectrum. The 

 same is true of other metals. Bunsen and Kirchoff made pioneer 

 investigations into the spectra of many terrestrial substances and 

 proved the presence of many of them in the sun. 



The matter was followed up by Angstrom in 1868 when he 

 published a map of the normal solar spectrum, in which the lines 

 were given wave-lengths. Thalen extended the work by deter- 

 mining the wave-lengths of the spark spectra of all the metals then 

 known and referring the values to Angstrom's normal map. The 

 use of photographic methods enabled Rowland to produce much 

 better maps and the wave-lengths of the solar lines in the visible 

 region of the spectrum were put on a more satisfactory basis. 

 Kirchoff's discovery of the meaning of the Fraunhofer lines in the 

 sun's spectrum naturally led up to attempts to observe the spectra 

 of stars. 



Sir William Huggins with Dr. Miller, and Sir Norman 

 Lockyer in England, Rutherford in America, Secchi in Italy, and 

 Vogel in Germanv were the pioneers in this "New Astronomy." 

 In the words of Huggins: "The time was, indeed, one of strained 

 expectation and of scientific exaltation for the astronomer, almost 

 without parallel; for nearly every observation revealed a new fact, 

 and almost everv night's work was red-lettered by some discovery. 

 And yet, notwithstanding, we had to record that the enquiry in 

 which we had been engaged has been more than usually toilsome ; 

 indeed it has demanded a sacrifice of time very great when com- 

 pared with the amount of information we have been able to 

 obtain." 



Huggins' first observation of the spectrum of a nebula is of 

 interest; he says: "Soon after the completion of the joint work 

 of Dr. Miller and myself, and then working alone, I was fortunate 

 in the early autumn of the same year (1864) to begin some observa- 



