326 Scientific Intelligence. 



author found that similar preparations had been made by earlier 

 observers, especially Norremberg, and Bertin. Braun extends 

 their work and shows that one of his preparations 2*8 mm thick 

 gave rings equal to those produced by a plate of apatite half 

 as thick ; or a plate of calcite, o*l mra thick. — Ann. der Physik., 

 No. 2, 1905, pp. 278-281. j. t. 



9. Emission Spectra of the Metals in an Electric Oven. — 

 Spectroscopic observations conducted with the electric arc and 

 spark are conditioned to a great degree by electrical phenomena 

 which are difficult to isolate from the mere effect of heat. A. S. 

 King has developed an electric oven similar to one used by 

 Liveing and Dewar, in order to excite emission spectra only 

 through heat. The forms of oven are described at length. The 

 vapors of the metals emitting spectra are formed close to the 

 hot carbon electrodes in these ovens. A resistance oven is also 

 described in which the heat developed by the white-hot resistance 

 excites the emission spectra. Many interesting results were 

 obtained which are summed up as follows : 



1. The oven affords emission spectra which in intensity differ 

 widely from those obtained in the electric arc. 



2. The method is especially suited for the observation of band 

 spectra. 



3. The changes in the series spectra of caesium show that the 

 glowing vapor follows the radiation law of solid bodies. 



4. Comparison of series lines in arc and spark spectra of differ- 

 ent elements shows that changed electrical conditions can work 

 in the same way as changed temperature conditions. 



5. The calcium spectrum in the oven shows a particular rela- 

 tionship of the lines H and K which appear weakly only at the 

 highest temperature. The ^-line shows an unsymmetrical broad- 

 ening of the reversal so that it appears to be displaced. The 

 vapor of the oven shows a much greater absorption power for g 

 than for the other lines of the spectrum ; this line varies with 

 the temperature. 



6. The homologous pairs in the spectrum of Ca, Sr, Ba, with 

 like magnetic types, are relatively much weaker in the oven than 

 in the arc. 



7. The oven spectrum gives new bands in the spectra of Ca, 

 Sr, Ba, and Cu. In the green-band group of Ba, there is an 

 apparent displacement of the position of maximum intensity from 

 band to band. 



8. The relative intensities of the Cu-lines of the oven approxi- 

 mate to those in a weak arc ; the absence of ultra-violet pairs 

 indicates temperature as the source of the radiation. 



9. In many cases only a trace of a substance is sufficient to 

 evoke characteristic lines. 



10. It is shown that ionized steam, which arises from the arc 

 but is separated from it, gives the arc spectrum even when it 

 lies outside the path of the current. 



