788 The Bight Hon. Lord Bayleigh [June 10, 



the water of combustion, seeing that the lowest part of the flame was 

 many inches higher. But desiccation of the gas on its way to the 

 nozzle was no remedy, and it was soon afterwards observed that no 

 dewing ensued if the flame were all the while under excitation, either 

 from excess of pressure or from the action of sound. The dewing 

 was thus connected with the unexcited condition. Eventually it 

 appeared that the flame in this condition, though apparently filling 

 up the aperture from which it issues, was nevertheless surrounded 

 by a descending current of air carrying with it part of the moisture 

 of combustion. The deposition of dew upon the nozzle was thus 

 presumably the source of the trouble, and a remedy was found in 

 keeping the nozzle warm by means of a stout copper wire (not 

 shown) conducting heat downwards from the hot tube above. 



The existence of the downward current could be made evident to 

 private observation in various ways, perhaps most easily by pro- 

 jecting little scraps of tinder into the flame, whereupon bright sparks 

 were seen to pass rapidly downwards. In this form the experiment 

 could not be shown to an audience, but the matter was illustrated 

 with the aid of a very delicate ether manometer devised by Professor 

 Dewar. This was connected with the upper part of the brass tube 

 by means of a small lateral perforation just below the root of the 

 flame. The influence of sound and consequent passage of the flame 

 from the unexcited to the excited condition was readily shown by 

 the manometer, the pressure indicated being less in the former state 

 of things. 



The downward current is evidently closely associated with the 

 change of appearance presented by the flame. In the excited state 

 the gas issues at the large aperture above as from a reservoir at 

 very low pressure. The unexcited flame rises higher, and must 

 issue at a greater speed, carrying with it not only the material 

 supplied from the nozzle, and constituting the original jet, but also 

 some of the gaseous atmosphere in the cavity surrounding it. The 

 downward draught thus appears necessary in order to equalise the 

 total issue from the upper aperture in the two cases. 



Although the flame falls behind the ear in delicacy, the combina- 

 tion is sufficiently sensitive to allow of the exhibition of a great 

 variety of interesting experiments. In the lecture the introduction 

 of a threepenny piece into one of the cups of a Hughes' induction 

 balance was made evident, the source of current being three 

 Leclanche cells, and the interrupter being of the scraping contact 

 type actuated by clockwork. 



Among other experiments was shown one to prove that in certain 

 cases the parts into which a rapidly alternating electric current is 

 divided may be greater than the whole.* The divided circuit was 

 formed from the three wires with which, side by side, a large flat 



* See 'Phil. Mag' vol. xxii. p. 490 (18SG). 



