Chemistnj and Physics. 235 



plate and hence they were negatively electrified. Only a few of 

 the particles pursued an undeviated course and were accordingly 

 neutral. With hydrogen at 13 mm. dark space the luminous 

 particles were practically all negative, the neutral particles 

 having disappeared. With the same gas at 25 mm. dark space 

 a few positive particles made their appearance. When the dark 

 space, was 51 mm. in hydrogen (the lowest pressure practicable 

 with the apparatus) the number of positive particles had 

 increased markedly, but the negative ones still predominated. 

 With oxygen at 6 mm. dark space the negative particles were 

 somewhat more conspicuous than the positive particles, whereas 

 at 13 mm. and 25 mm. the positive and negative centers pro- 

 duced about equal photographic impressions. With carbon 

 dioxide at 25 mm. the two kinds of charged particles were 

 equally conspicuous. In the case of nitrogen at 25 mm. the 

 positive particles slightly exceeded the negative ones in luminous 

 effect. Mercury vapor at 19 mm. gave negative centers only. 

 At 32 mm. dark space this vapor showed also a trace of positive 

 particles. At 38 mm. the proportion of positive particles had 

 increased noticeably. The final explanation of these phenomena 

 has not been found, but Strutt favors the opinion that the 

 luminosity must have been stimulated in the particles before they 

 entered the electrostatic field and therefore the luminosity of the 

 deflected streams cannot be due to ionization by recombination. 

 The next experiments described correspond to relatively high 

 pressures and a different form of apparatus. A spark was 

 passed, in the gas under investigation, between iron wires the 

 ends of which were 1 cm. apart. These wires ran along the axis 

 of a silica tube of 1-5 mm. inside diameter. A hole of about 

 0-7 mm. diameter was pierced in the wall of this tube opposite the 

 middle of the spark gap. The silica tube passed eccentrically 

 across a right section of a larger cylinder having a transparent 

 window at one end, etc. Hydrogen gave far more striking 

 effects with the condensed than with the uncondensed discharge. 

 The best results were obtained with a pressure of 17 cm. in the 

 silica tube and 2 or 3 mm. in the outer cylinder. ' ' In this case a 

 tongue of flame of a beautiful rosy colour, and about 9 mm. 

 long, was seen issuing from the hole." The spectrum of this jet 

 shows the Balmer series lines without the usual background of 

 the band spectrum. Strutt was able to photograph the first ten 

 series lines. He also found that the width of the spectral 

 lines was much less in the jet than in the condensed spark 

 where the luminosity had been excited. Stark has given reasons 

 for believing that the broadening of spectral lines is due to the 

 electric fields of neighboring atoms. "It is, therefore, not sur- 

 prising that the removal of these to a greater mean distance, 

 when the gas issues from the hole and expands, should cause the 

 lines to become narrow." 



