158 THE SCIENTIFIC PAPERS OF 



at present limited to the small cylindrical surface exposed to the 

 steam by the short length of central jet intervening between the 

 water nozzle and the receive nozzle of the discharge pipe. This 

 seemed to him an extremely small surface for absorbing such a 

 large amount of heat as had to be taken up by the steam ; and he 

 thought that better results in condensation of the steam, together 

 with some economy of condensing water, would be obtained, if 

 the surface of the water jet could be largely increased, without 

 altering the apparatus in other respects. Such an increase of 

 surface he suggested might be obtained by making the water jet 

 annular, and introducing the exhaust steam by a central jet inside 

 the annular water jet, as well as outside it as at present. The 

 steam would then be condensed both by the internal and external 

 surface of the annular water jet, instead of only by the external 

 surface of the present solid jet ; and judging from the experiments 

 he had made with an annular steam jet for the propulsion of air, 

 he believed the condensing action of the annular water jet would 

 be much more efficacious and prompt. He inquired whether any 

 trial had been made of the annular water jet. 



The President observed that in the experiment which had been 

 described with a small tube inserted up the centre of the dis- 

 charged jet, it was to be expected that, if the height of the top of 

 the tube were such that it encountered the water of the jet after 

 this had had its motion accelerated by the propelling action of the 

 steam, the great momentum of the water moving at so high 

 a velocity would produce a high pressure by impact upon the 

 orifice of the tube ; but if the tube orifice Avere raised a little 

 higher, it would be clear of the water, and would be exposed only 

 to the central jet of boiler steam, at the point where that steam 

 was itself undergoing condensation by the water jet, and where 

 consequently there would be more or less of a vacuum, as had 

 been mentioned to be the case. He did not think, however, that 

 there could be any piercing of the water jet by the steam in the 

 condenser, but only an interchange of particles between the colder 

 water in the centre of the jet, and the hotter external portion, 

 which was essentially a gradual process; and the larger the 

 diameter of the solid jet, the greater would be the difference of 

 temperature between the internal and external portions, and the 

 greater would be the loss of condensing water. 



