450 Prof. Wiillner on M. Goldstein's Observations 



mann, which, as it seems to me, pretty well elucidate the phe- 

 nomena in question. 



The tube used for these experiments had a uniform diameter 

 of 2 centims., the points of the electrodes being 8 centims. 

 distant from each other. Besides the tube, a Riess spark- 

 micrometer was placed in the circuit, by which such spark-dis- 

 tances as I pleased could be inserted. The method of conducting 

 the observations was that which I had previously employed, and 

 is described in Pogg. Ann. vol. cxlvii. 



If the exhaustion of the tube was a minimum, with a long 

 spark-distance the discharge passed only in the same rhythm as 

 in the spark, but it filled the entire tube ; the spectrum is not 

 the line-spectrum, but the band-spectrum not sharply shaded. 

 If the spark-distance be diminished, there follows upon the first 

 momentary discharge a positive luminous tuft showing stratifi- 

 cation (that described in the Jubelband of PoggendorfFs Anna- 

 len). The number of strata increases as the spark- distance 

 decreases ; when the distance is short, but still just sufficient to 

 exclude the closing-current, four strata are visible. 



At about 1 millim. pressure, if a spark-distance of 30 millims. 

 be inserted, the discharge commences with a momentary partial 

 discharge which fills the tube, followed immediately by a positive 

 luminous tuft with stratification. The spectrum is the band- 

 spectrum. With decreasing spark-distance the stratification 

 becomes sharper, and in the spectrum the shadings appear more 

 distinct. 



With an air-pressure of 4 millims. and without a spark- 

 distance the positive tuft, completely filling half of the tube, 

 appears as a perfectly continuous field of light ; but when a 

 spark-distance is inserted, first the momentarily passing bluish 

 discharge shows itself, and the positive tuft takes the form of a 

 cloud (described by P. A. in the Jubelband). Band-spectrum. 



Pressure 25 millims. A small spark-distance gives at the 

 commencement a partial discharge, visible in the rotating mirror 

 as an unspread image of the tube; then follows a luminous tuft 

 at the positive electrode in the form of two clouds. If the spark- 

 distance is taken very great, only the momentary partial dis- 

 charges appear, which fill the tube each time with whitish blue 

 light. In the spectrum the shadings are no longer distinctly 

 recognizable; but not a line of the line-spectrum is to be seen. 



Pressure 45 millims. Without a spark-distance the light 

 divides in the rotating mirror into four clouds. With a spark- 

 distance of 30 millims. the clouds have nearly vanished, and the 

 current passes only in 3-4 discharges, which in the rotating 

 mirror give unspread images of the tube ; but the spectrum is 

 still the band- spectrum, only not so sharply shaded. On 



