904: Prof. Wood and Mr. Hemsalech on Fluorescence 



with oxygen in the jet-box, the streamers being due solely 

 to light from the spark scattered by the cloud of small par- 

 ticles which forms almost immediately in this gas. The 

 presence of scattered light (i. e. diffused by dust) can always 

 be recognized by a very intense streamer above the violet 

 region of the spectrum (marked V. in PL XIV. fig. 1). It will 

 be observed that this streamer is absent in all the other photo- 

 graphs. Fig. 3, PL XIV. was made with 00 2 in the jet- 

 chamber. Here we have a single streamer practically in 

 coincidence with the left-hand streamer in fig. 1, which 

 is due to the scattering of the strong copper lines 3292 

 and 3247. Higher dispersion would show this streamer 

 double, the copper lines falling midway between the two 

 bands. Later on we shall refer to the spectrum of the jet 

 in CU 2 made with a quartz spectrograph. 



Fig. 3 shows the jet in nitrogen, the spark-chamber being 

 flooded with oxygen during the exposure. The nitrogen 

 was obtained from a bomb of compressed gas, and contained 

 some oxygen. The strongest streamer, immediately above 

 the black dot, is the so-called water-band, while the three 

 bands to the right (position indicated by vertical lines) are 

 the nitrogen bands. This photograph shows us that the gas 

 in which the spark passes is practically without influence 

 upon the intensity or the spectrum of fluorescence of the gas. 

 in the jet-chamber. Very remarkable is the jet shown in 

 fig. 4, also made with nitrogen. In this case the strong- 

 streamer to the right appears to coincide with the third 

 nitrogen band (longest wave-length) of fig. 3, which is very 

 faint in fig. 3. In fact, it is doubtful if the nitrogen bands 

 of fig. 3 will appear in the reproduction. Why this streamer 

 is of such great intensity we are unable to say. The previous 

 experiment was, however, made with coal-gas, and we feel 

 inclined to attribute this streamer to some impurity left in 

 the jet-chamber or rubber tube. Xo trace of the streamer 

 appeared, however, in cases in which the jet-chamber was 

 filled with coal-gas, as appears from fig. 14, PL XV., in which 

 we have two streamers, one to the right and one to the left 

 of the position occupied by the water-band. 



With a current of hydrogen flowing through the jet- 

 chamber (fig. 16, PL XV.), we have a streamer in the same 

 position as the C0 2 streamer. The hydrogen and C0 2 were 

 both obtained from bombs, and it is quite possible that some 

 impurity, such as a volatile constituent of the oil used for 

 lubricating the compression-pumps, may be present in each. 



It will be impossible to make any very positive statements 

 until the experiments have been repeated with pure gases. 



