AMERICAN INSTITUTE. , 593 



inconvenience of arrangement. The objections to this plan have 

 already been alluded to. All stone or other masonry is, to a cer- 

 tain extent, a conductor and consequently an absorbent of caloric. 

 The noted pendulum experiment in Bunker Hill monument, 

 demonstrated the fact of the alternate expansion and contraction 

 of the sides of that structure, in perfect accordance with their 

 exposure to the bright sunshine. Increasing the thickness of 

 walls will, of course, prolong the time necessary to heat them 

 through, but it produces another eifect which fully counterbal- 

 ances this advantage. It renders their temperature more uni- 

 form, and, of course, more nearly the average of the temperatui'e 

 of the open air day and night the whole year round. This is so 

 far below that which is required in occupied apartments, that the 

 interior of such walls are almost always cold, and, as a conse- 

 quence, damp ; for the air which has been rarifled in a warmer 

 place, and charged to its capacity with moisture at that heat, 

 will, on being brought in contact with a cold wall, lose its reten- 

 tive power, and its vapors will be condensed upon the cold sur- 

 face, to be again evaporated at the next fall of the mercury. 



To obviate these objections, hollow bricks have been used to 

 reduce the mass of masonry, while strength and thickness of wall 

 is retained. To the extent of the material removed, this plan may 

 be effective in this respect, no more. Even hollow walls bound 

 together by bricks, will show on warm, damp days, through the 

 plaster coating, where the bond bricks are placed. 



For health, as well as comfort then, we need for our protection, 

 some substance which is neither a conductor nor an absorbent 

 of radiated heat. It is also important that this material should 

 be easily and cheaply obtained and applied. Better than any other 

 known substance, answering the required conditions most per- 

 fectly in every respect, and free as the air we breathe, the desired 

 material is everywhere at hand. 



It has long been known that confined air was among the best 

 non-conductors of caloric — that this fact has not been more ap- 

 plied to practical purposes, is in a great measure owing to a 

 failure to distinguish between confined air and circulating currents. 

 The latter may answer a good purpose in their way for heating 

 or ventilation, but the former affords the nearest approach to a 

 perfectly non-conducting wall which has yet been produced. It 

 neither conveys the heat from the one side to the other, nor does 

 it retain it to give it out again as occasion may arise. To render 

 walls perfect protectors between heat and cold we believe it is 



[Am. Inst.] 38 



