252 CARNEGIE INSTITUTION OF WASHINGTON. 



Infra-red Furnace Spectra. 



Plates bathed with dicyanin were used in this investigation, the 

 object of which was the extension into the infra-red of the data on the 

 temperature behavior of spectral lines. Seventy-one spectrograms 

 were made, the elements studied being iron, titanium, nickel, cobalt, 

 barium, strontium, and calcium. The furnace spectra thus obtained 

 extended to about X9200. Within this limit, a large proportion of 

 the lines observed in the arc were regularly obtained with the furnace, 

 together with fainter arc-lines which the furnace produces with 

 relatively high intensity. Spectra were photographed at three tem- 

 peratures and for the most part with two different spectrographs. 

 The lines were classified according to the temperature at which they 

 appear and the rate of increase of intensity with temperature, in the 

 same way as in previous work. The low-temperature lines thus 

 segregated will be of interest when a more extended study of stellar 

 and sun-spot spectra for this region has been made. The high-tem- 

 perature lines, weak or absent in the furnace spectrum, are also im- 

 portant. Among these are the three strongest lines in this region 

 of the solar spectrum. They belong to calcium and are strongly 

 enhanced lines. The temperature classification is also proving useful 

 in the selection of series lines in the case of barium and strontium. 



Absorption Spectra with the Electric Furnace. 



A graphite plug placed in the central portion of the furnace-tube 

 gives an incandescent background for the radiating vapor and pro- 

 duces an absorption spectrum which may be examined at the same 

 temperatures as are employed for emission spectra when the plug is 

 not used. Many interesting features appear in the 54 spectrograms 

 thus far made, chiefly of iron and titanium. A pure absorption spec- 

 trum is observed, no emission lines or bands appearing, thus indicating 

 that the radiation of a black body, which the plugged tube closely 

 approximates, is stronger than that of a vapor when excited by the 

 same degree of temperature. Furthermore, striking differences appear 

 between the absorption spectrum and the emission spectrum which 

 can be photographed at the same temperature by removing the plug. 

 For a given temperature, the absorption lines are fewer in number 

 than the emission lines, and the absorption lines which do appear are 

 those of the emission spectrum at a much lower temperature. Thus 

 a temperature which produces a rich emission spectrum gives in ab- 

 sorption only the low-temperature lines. As the temperature is raised, 

 other groups appear, which belong to successively higher temperature 

 classes. The method gives a close measure of the absorptive power 

 of each spectrum line, and the grouping arranged on this basis is found 

 to be in complete agreement with the temperature classification already 



