162 On the Electrification of a Steam-jet. 



fore necessary to hold them on one side, and direct their 

 heated gases upon the jet by blowing or fanning. 



After reading Helmholtz's paper it naturally occurred to 

 me to try the effect of combustion upon the water-jet. In 

 this case the objection to the use of an actual flame does not, 

 of course, apply. I therefore introduced the flame of a 

 Bunsen burner into the jet, and found that, if the air-holes 

 were stopped up, and the flame thus rendered luminous, a 

 decided effect was produced upon the jet. Often, indeed, it 

 became just as completely coherent throughout its length 

 as if it were electrified, though I have not yet succeeded in 

 obtaining tins result with perfect certainty ; but in every case 

 when the burner was held a little below the point of resolu- 

 tion, a considerable diminution, of the scattering was observed. 

 If the air-holes were opened and the flame made non-luminous, 

 it failed to act in any way whatever upon the jet. It is to 

 be remarked that Helmholtz found certain non-luminous 

 flames (of which, however, a gas-flame was not one) to be 

 devoid of influence upon the steam-jet. 



Can the effect here also be due to electrification"*? It 

 can hardly be attributable to heating, because the flame of 

 a Bunsen burner is certainly hotter when it is non-luminous 

 than when it is luminous. On the other hand, it is known 

 from many experiments that flame is electrified. If, for 

 example, we place a luminous flame between the positive and 

 negative ball- terminals of a Yoss machine in action (the ter- 

 minals being too far apart for sparks to pass), we find that 

 the flame, or at least the upper part of it, is repelled by the 

 positive and attracted by the negative ball. This seems to 

 denote positive electrification of the flame. 



In conclusion, it should be mentioned that Helmholtz 

 suggests another hypothesis as an alternative to that of mole- 

 cular shock, though he does not appear to attach much impor- 

 tance to it. It is that the electrical discharge, the flame or 

 other exciting agent, whatever it may be, acts by introducing 

 into the steam-jet minute particles of solid matter which serve 

 as nuclei upon which the water-vapour may condense, as in 

 Aitken's experiments on the formation of fog. 



It is possible that several different causes may be competent 

 to produce the condensation phenomena. 



* In replying to the discussion which followed the reading of the paper, 

 I suggested the possibility, which had occurred to me after it was written, 

 that the flame might act simply by coating the separate particles of water 

 with certain products of combustion, Lord Eayleigh haying found that 

 the addition of a little soap or milk to the water prevented the scattering. 

 Perhaps the action of flame upon the steam-jet may be similarly explained. 



