Hydrogen in the O.vyhydrogen Flame. 373 



cases even longer, but no one of these showed a trace of the 

 hydrogen-lines H y , H 5 , or H e *. Other photographs of the 

 spectrum of the flame extended as low as D, but these like- 

 wise showed no trace of any hydrogen-line. If the rays were 

 emitted at all by the flame, though so faint as not to be de- 

 tected by the eye, they must surely have depicted themselves 

 on the photographic plate with so long an exposure. 



However, it might have happened, though it is not likely, 

 that there was something in Pliicker's arrangement which 

 had enabled him to get the lines, while I failed. So I have 

 made a new series of direct observations of the flame in order 

 to make sure. Unfortunately, Pliicker's mention of his ob- 

 servations is an episode, and he does not describe his appa- 

 ratus. He merely says that he allowed the two gases, from 

 two gasometers, to flow together, and inflamed them, and 

 endeavoured so to regulate the pressure that the excess of 

 hydrogen should be heated as much as possible by the flame. 

 He succeeded in getting a red tip to the flame, and a Babinet's 

 goniometer showed H a and Hp. 



I have tried three forms of jet, ail of platinum. First a 

 double jet, one tube within the other, and hydrogen supplied 

 through the inner tube, oxygen through the outer ; also the 

 same with hydrogen outside and oxygen inside. Secondly, a 

 jet in which the two gases were mixed in a small chamber, 

 and the jet of mixed gas burnt. Thirdly, two streams, one of 

 oxygen and the other of hydrogen, were allowed to impinge 

 on one another at an angle of about 45°, so as to form a fish- 

 tail flame. 



I used two spectroscopes. The telescopes of one had 

 object-glasses 1\ inches in diameter, with two prisms of 30° 

 of similar aperture, fixed one in front of each object-glass and 

 carried with the telescope, so that the spectrum was always 

 of the greatest purity and the light ample. I used also an 

 eyepiece of low power, so as to have every chance of detect- 

 ing faint lines. 



The other was smaller. It was a direct-vision spec- 

 troscope with two Christie half-prisms, of which the second 

 was in the reversed position, so as to give a pure spectrum 

 though no great dispersion : an excellent instrument for 

 detecting faint diffuse lines or bands. 



In observing, the instrument was set and focused for the 

 F, or C, line of the solar spectrum, and then turned to the 

 flame, and the room darkened. 



* This is following Pliicker's notation, so that H« stands for the 

 hydrogen-line corresponding to the Fraunhofer line H. 



Phil. Mag. S. 5. Vol. 34. No. 209. Oct. 1892. 2 D 



