14 THE SCIENTIFIC PAPERS OF 



tion) would, it is presumed, proceed with undefined rapidity, if 

 it were not retarded by the second and third, or by the presence 

 of some permanent gases, which accumulate on the condensing 

 surfaces and prevent their immediate contact with the steam. The 

 second (conduction) varies in direct proportion with the conduct- 

 ing power of the metal, and with its thickness ; but the conducting 

 power of copper is so great that its thickness seems to exercise no 

 appreciable influence on the amount of heat transmitted in a given 

 time. This interesting fact is proved by Dr. lire's experiment 

 with two copper pans, of the same internal area, but very unequal 

 thickness of bottom, the thicknesses being in the proportion of I 

 to 12 ; which were both filled with water, and dipped into a hot 

 solution of muriate of lime. It was found that the water in the 

 thick pan evaporated the quickest, which may be accounted for by 

 its slightly increased external surface in contact with the heating 

 solution ; and this affords additional evidence that the limit of 

 transmission does not lie within the metal, but rather between the 

 metal surface and the liquid. That the absorption of the heat by 

 the water is a slow process may be inferred from the circumstance 

 that water, although possessing a large capacity for heat, is a very 

 bad conductor, and depends for its power to absorb heat on the 

 slow circulation over the heating surface caused by the lower 

 specific gravity of the heated particles of water. A strong artificial 

 current along the heating surfaces greatly accelerates the process. 



The surface condenser above described was arranged in accord- 

 ance with these observations. It contains : heat-absorbing surfaces 

 (by the water), 18 square feet per horse power ; condensing sur- 

 faces, 9 square feet per horse power ; computed mean thickness 

 of metal through which the heat is transmitted, 1| inch ; weight 

 of copper, 60 Ibs. per horse power ; space occupied by plates, 0'4 

 cubic foot per horse power, or about one-tenth of the space occupied 

 by the tubes in the tubular condenser. 



The essential features of this condenser are its comparative 

 cheapness of construction, and the easy access which it affords to 

 the water channels between the plates. It also requires less con- 

 densing water than previous surface condensers, in consequence 

 of the repeated and close contact in which each particle is brought 

 with the heating surfaces, before it can reach the upper reservoir 

 or hot well. The author considers that the surface condenser just 



