274 CARNEGIE INSTITUTION OF WASHINGTON. 



to one atmosphere, the enhanced lines steadily weakened, while the 

 characteristic arc lines retained their full intensity. Variation of the 

 amount of titanium vapor produced no material change in the strength 

 of the enhanced lines. This evidence, in conjunction with the known 

 phenomena of the arc and spark, points to a dependence of the enhanced 

 lines upon the presence of high-speed electrons, which are known to 

 be expelled from highly-heated matter and to be favored by reduced 

 pressure. 



DISSYMMETRIES PRODUCED BY THE SPARK DISCHARGE. 



A preliminary set of observations, based on 77 photographs, has 

 been made by Mr. King on the effect of a powerful condensed spark in 

 rendering spectrum lines unsymmetrical to such a degree as to give 

 virtual displacements when measured. Selected regions of the iron 

 and titanium spectra from X 3600 to X 6500 were observed for the 

 general character of the effect, its variation for lines of different classes, 

 and its change with the wave-length. The use of high dispersion with 

 the plane-grating spectrograph showed that the inner vapor of the 

 spark produces a dissymmetry giving an apparent displacement toward 

 the red, while that of the outer vapor gives lines coinciding with the 

 arc. The low-temperature furnace lines and the enhanced lines show 

 but slight susceptibility, while the varying degree to which other lines 

 are affected appears to be closely related to their furnace classification. 

 A few lines are unsymmetrical toward the violet. For iron and tita- 

 nium the lines most strongly affected are in the region of shorter wave- 

 length. This feature and the behavior of individual lines are against 

 a direct relation w4th the pressure-effect, as is also the fact that the 

 spark dissymmetry appears to agree in all details with that observed 

 with the tube-arc in vacuo at low potential. Tests with polarizing 

 apparatus gave no evidence of a connection with the effect of a strong 

 electrical field observed by Stark. A quantitative study will be made 

 with the registering micro-photometer. The subject has important 

 astrophysical bearings, owing to the fact that the displacing agency 

 in the spark may also be active in stars whose spectra show strong 

 enhanced lines and thus indicate a condition in some respects similar 

 to that of the spark. 



VACUUM-ARC OBSERVATIONS. 



A series of photographs of the vacuum-arc spectra of chromium and 

 iron has been made by Mr. King. For some of the diffuse chromium 

 lines the well-known narrowing effect of reduced pressure was found 

 to be very pronounced and improved wave-length measures have been 

 made. Many intensity differences for both chromium and iron appear 

 between the vacuum arc and that in air. A reddish discharge at the 

 positive pole of the iron arc was found to be due to a high intensity of 

 the Ha line. This part of the arc gave also strong bands of nitrogen, 

 of which high-dispersion photographs were obtained. 



