402 PROCEEDINGS OP THE AMERICAN ACADEMY. 



" cold spark." In view of this fact we have employed these three bauds 

 as standards of intensity ; and have called any two spectra of " equal 

 intensity " when these three bands were of equal intensities on the 

 respective negatives. Each member of the series was, in this way, made 

 of practically the same intensity. 



As to the carbon lines, very few appear in this region. The line at 

 A 4556.3 does not appear in the hot spark, i. e. in the earliest phase of 

 the series described above. The broad hazy line at A 4267.5, which Eder 

 and Valenta * call the " chief carbon line," disappears completely on 

 introducing inductance into the circuit of the cold spark. And it does 

 not appear at all in the hot spark. These two facts raise the question 

 as to whether this Hue is due to carbon. The line at A 3361 persists in 

 the hot spark ; but it also appears in the aluminium spark and, greatly 

 enhanced, in the copper spark when there is no capacity in the circuit. 

 As to the remaining lines which Eder and Valenta describe in this region 

 AA 3920.8, 3877.0, and 3848.0, they are weak, and we have not been 

 able to identify them to our satisfaction. 



II. Air Lines and Flutings. 



Not one of the ordinary air lines appears on any photograph whose 

 phase is earlier than § second. On the plate whose phase is f second 

 appear only the very heaviest of the air lines, viz., AA4630: 4447: 

 3995 : 3433 : 3330. Indeed the elimination of air lines is so complete 

 in these earlier phases that non-appearance in the hot spark might be 

 used as one criterion for air lines, analogous to the inductance test dis- 

 covered by Schuster and Hemsalech. 



As to nitrogen flutings which appear in spark spectra, when the 

 electrodes are close together or when inductance is placed in series with 

 the condenser, the case is very different — quite reversed, indeed — from 

 that of ordinary air lines. The nitrogen flutings with heads at AA 3371.1 

 and 3158.7 respectively come out very strong in the earliest phase; at 

 % second they begin to weaken ; after 3 seconds, only a trace of them is 

 left. 



The nitrogen flutings of wave-length longer than 3371 do not appear 

 in the spark under the conditions in which we are working, namely, a 

 3-millimeter spark gap in series with a condenser of ■£$ microfarad 

 capacity ; no inductance. 



We have not found any description of these nitrogen bands as they 



* Eder and Valenta, Denksch. K. Akad. Wien, 60, 249 (1893). 



