i.:,li:KICAN INSTITUTt:. 



591 



posed may differ greatly in their character, and the costliness and 

 mode of construction may be as various ; but the same natural 

 laws will apply to all, .and are to be alike studied by the buildejs 

 of every class of structures. The mode of their application is to 

 be determined in each case, according to its peculiar circum- 

 s.'auces. 



In building, as in many other arts, failure is often caused by 

 ati endeavor to accomplish something before unknown, or to 

 arrive at results by principles and methods entirely new. In the 

 few hints which follow attention will be turned the other direc- 

 tion, in the hope well known principles, and the most commonly 

 observed facts, may suggest the means of improving our dwellings 

 by simple and easy processes — a matter in which all who live 

 under roofs have a personal interest. 



The precaution most obviously necessary in building is that 

 against the direct intrusion of rain or wind from without. The 

 prevention of this evil is simply in walls and roofs, air and water 

 tight; and while they remain so, whatever their nature in other 

 respects may be, their purpose in this regard is answered. But 

 other hostile influences are more subtle. It is the impenetration 

 of heat, or caloric, without the actual passage of air or water, 

 that presents to us the greatest difiiculties, by increasing the 

 temperature of oiu* apartments in w^arm weather or depriving 

 them of their heat in winter. This in two ways greatly difier- 

 ent in their effects and in the means required for their counter- 

 action. 



The first is by direct radiation. Radiated heat is only trans- 

 mitted through transparent media which are themselves not 

 affected by it. As but a small portion of ordinary buildings is 

 of this character, the trouble from this cause is comparatively 

 small, and easily avoided by curtaining the windows. The air 

 of the interior being transparent, is but little affected by radia- 

 tion either of solar heat or that artificially produced. 



The other source of difficulty is the transmission of heat 

 through conducting substances. That we may the better under- 

 stand the operation of this influence, let us take two extreme 

 cases and analyse the facts in each. The walls of the Merchants' 

 Exchange are of solid masonry, in great part granite, of enormous 

 thickness. Within the building, whatever may be the changes 

 in the external atmosphere, the temperature is equable, never 

 reaching within several degrees of the extremes of the seasons, 

 and in its changes much slower than that of tlie open air. The 



