\\-II.I.lAM SIEMENS, F.R.S. 13 



circulates. These tubes are surrounded by cold water, which fills 

 up the space between the flat chests. A small air pump removes 

 the condensed water and air from the lower chest. The great 

 weight and cost of this condenser, its liability to derangement, and 

 the impossibility of removing the calcareous deposit of the water 

 from the tubes without taking the whole fabric to pieces, are found 

 to be serious practical objections. 



In the year 1847 the author had occasion to apply a surface 

 condenser in a situation where economy of space and material 

 were essential. In considering the most rational distribution of 

 surfaces, he happened to find an arrangement which, with less than 

 one half the amount of material used in Hall's condenser, produced 

 a very satisfactory result, and which paved the way to the more 

 important improvement chat forms the principal subject of this 

 paper. 



The surface, condenser referred to, shown in Figs. 4 and 5, 

 Plate 2, consists of a number of copper plates A A, of ^Vnds inch 

 thickness and about 4 inches broad by 2 feet long, which are 

 fixed together by two longitudinal flattened wires of the same 

 metal between the adjacent plates ; and the whole pile is screwed 

 up tight together between the sides of a rectangular cast iron 

 vessel, which constitutes the body of the condenser. The ends of 

 the plates project through the top and bottom of the condenser, 

 and are planed flush with its exterior surfaces. The joints at top 

 and bottom are secured by means of india-rubber rings, which are 

 screwed down under small cast iron frames, and yield to the 

 difference of expansion between the two metals. The flattened 

 wires are laid parallel, about 3 inches apart from each other, and 

 form with the plates a large number of narrow passages, through 

 which the cold condensing water flows in a vertical direction, 

 without entering the vacuous space of the condenser, into which 

 the edges of the plates outside the flattened wires project, forming 

 the condensing surfaces. 



The rationale of this condenser is as follows. The transmission 

 of heat in a surface condenser is threefold : first, from the con- 

 densing steam to the internal metal surfaces ; secondly, from the 

 internal surfaces through the body of the metal to its external 

 surfaces ; and thirdly, from the external surfaces to the surround- 

 ing water by which it is carried off. The first operation (condensa- 



