908 



SCIENCE 



[N. S. Vol. XLIV. No. 1148 



be remarked that Fabry and Buisson have 

 concluded from measurements of the width 

 of lines that both spectra are due to emis- 

 sion centers of atomic size. From a study 

 of the displaced components of many ele- 

 ments, electronegative as well as electro- 

 positive, Stark concluded that in all cases 

 line spectra are emitted by positively 

 charged atoms. Aluminum atom ions may 

 have one, two or three charges, which ap- 

 pear in succession as the voltage is in- 

 creased. The same is true of argon. The 

 red spectrum is apparently due to singly 

 charged ions, the blue or spark spectrum 

 to multiple charges. Mercury may have 

 as many as four charges, each giving rise 

 to a characteristic group of lines, all those 

 due to multiple charges being spark lines. 

 From an examination of many such cases 

 Stark concludes that in general arc lines 

 or those of the positive column are due to 

 singly charged ions, sharp spark lines to 

 double charges, and diffuse spark lines to 

 triple charges. There are some apparent 

 exceptions to this classification, but in the 

 main the evidence seems to support his 

 views, which are also consistent with the 

 results obtained by Reichenheim from the 

 study of anode rays. For the first time we 

 are thus enabled to assign a common cause 

 for spark lines produced under apparently 

 very different conditions. They are found 

 in the spectra of disruptive discharges, of 

 the negative glow in vacuum tubes ; in the 

 intermittent or oscillating arc when rapid 

 changes in potential occur, although the 

 maximum potential may be small ; near the 

 poles of the arc, where the anode and 

 cathode potential gradients are steep ; in 

 the electric furnace when the temperature 

 is high; in high temperature stars, and, as 

 found by Hemsalech and de Watteville, 

 even in the green cone of the Bunsen flame, 

 where chemical action is energetic. In all 

 these cases we might expect multiple ioni- 

 zation to be favored. 



Similar conclusions regarding the charges 

 of emission centers may be derived from 

 observations by Stark, Child, Strutt and 

 others on the luminous vapors from an arc 

 between charged condenser plates. The 

 carriers of the line spectra are swept out 

 of the field, while the luminous vapors giv- 

 ing band spectra are unaffected; or, if the 

 lines of several series are present, their in- 

 tensities are modified in different degrees 

 by the electric field. Studies of the os- 

 cillatory spark by Schuster and Hemsa- 

 lech, Schenck, Milner, Royds and others 

 indicate that the spark lines do not per- 

 sist as long as arc lines. If the emission 

 centers of the former are multiply charged 

 this is what we might expect. 



Investigations on the mechanism of the 

 spark give results which at first sight seem 

 opposed to Stark's theory. All observers 

 agree that the luminous vapors appear to 

 be projected from the cathode, with dif- 

 ferent velocities for different lines, and 

 the tacit assumption seems to have been 

 made that they are negatively charged. 

 That metallic vapors are projected from 

 the cathode is evident from the fact of 

 cathode disintegration, and probably the 

 particles are initially negatively charged. 

 We know very little concerning this phe- 

 nomenon, but two things are almost cer- 

 tain — that only a small fraction of the me- 

 tallic particles take part in the luminosity, 

 and that these particles are not negatively 

 charged while radiating. The large veloc- 

 ities indicated by the curvature of the 

 streamers viewed in a rotating mirror do 

 not give rise to a corresponding Doppler 

 effect, and it seems highly probable that 

 Hull and Royds are correct in their sur- 

 mise that what happens is really the 

 propagation of a condition of luminosity 

 through vapor which continuously fills the 

 gap after the first discharge. Electrons 

 initially projected with a high velocity, 

 which diminishes as the field intensity 



