WILLIAM SIEMENS, F.R.S. 191 



houses, so that it might be used for tho various purposes men- 

 tiuiu-d. The great question which presented itself was, would 

 such a pipe be trustworthy ; could it be laid and maintained for 

 this purpose without danger and without trouble. The paper 

 described an elaborate method of insulating the pipe to prevent 

 Mve loss by radiation, and from the figures given it seemed 

 to have been very successful ; but it appeared to him doubtful 

 whether, in our streets, a pipe so swelled out by insulators, and 

 logs of wood, and planks, could be laid. The space below our 

 streets was already so fully occupied, that the establishment of 

 such pipes would present very great difficulties. As Sir Frederick 

 Brain well remarked, if ,^hey wanted to bring heat into houses, 

 there was another means already established, and in full opera- 

 tion ; and from a little calculation he had just made, he found 

 that a cubic foot of coal-gas brought with it about 750 heat units, 

 which would be about the same amount as would be supplied by 

 8j cubic feet of steam, at a pressure of 6 atmospheres. The ques- 

 tion, therefore, would reduce itself to this, whether the one pipe or 

 the other could be maintained with the least expense. He, for 

 one, must adhere, for the present, to the opinion that it would be 

 easier to supply gas than steam. The paper spoke of various 

 modes in which steam heat could be used, and the radiator was 

 alluded to, but he did not think that apparatus was very happily 

 named. A steam-heated surface in a room no doubt radiated heat, 

 but not under the same conditions as a fire-place. Probably, nine- 

 tenths of the heat given off from that hot surface would be given 

 off to circulating currents of air, which would pass again and 

 again through this radiator, and a very small portion would pass 

 by radiation into the room. The rays from such a low source of 

 heat would hardly be felt, as radiant heat, at any sensible distance 

 from the source. Now, he looked upon an open fire-place not only 

 as a thing endeared to them by long habit, but he attributed to it 

 very high sanitary qualities. The open fire-place communicated 

 absolutely no heat to the air of the room, because air being a per- 

 fectly transparent medium, the rays of heat passed clean through 

 it. It gave heat only by heating the walls, ceiling, and furniture ; 

 and here was the great advantage of the open fire. If the air in 

 the room were hotter than the walls, condensation would take 

 place on them, and mildew and fermentation of various kinds 



