FROM DIFFERENT APPARATUS. 



chimney, is the same as the temperature of the atmosphere 

 No current of air would he found to pass either up or down 

 the chimney, hecau.se the pressure of the column of air in the 

 room would be counterbalanced by the equal pressure of ih< 

 column of air within the chimney, and. consequently, both 

 must remain stationary. If the temperature of the air within 

 the chimney he elevated by any means, it expands, and becomes 

 specifically lighter, and an ascending current will he produced; 

 and if the same elevation of temperature remain, and we sup- 

 pose any change, however great, in the pressure of the atmo- 

 sphere, as that change must, of necessity, operate on both 

 columns of air, consequently, the velocity of the current musl 

 remain the same. The current of air through a chimney, be- 

 ing wholly an artificial production, its velocity will always 1" 

 proportional to its temperature above that of the exterior air. 

 whereby the column of air in the chimney being rendered 

 lighter than the exterior column, yields to its superior pressure, 

 and thus the current is established. 



If the air in the room is warmer than that in the chimney, 

 a descending current will be produced ; which shows the pro- 

 priety of closing, during the winter season, those lire-places not 

 used, to prevent the descent of cold air and smoke from tin 

 adjoining flues; and the advantage of leaving them open during 

 the hot season, when the exterior.air is known to be at a Iowa 

 temperature than the r is with which they are connected 



The existence of counter currents in a chimney, when in use, 

 and properly supplied with air. spoken of by some writers llM 

 this subject, appears to he an illusion, produced by eddies in 

 the air. at the sides of the chimney, as it i at n from the room, 

 as it would be difficult to assign any satisfactory cause for such 

 an effect under the circumstances described. 



In ti^ht rooms, where fire-places are hit open, and are not 

 in use, counter currents will exist, so long as difference in tem- 

 perature exists between the air of the room and tin extern. d 

 atmosphere. 



In those instances where the room is too tight t<> admit ail 

 in sufficient <piantity to supply the current m ci ssarv '■■ ' ik< 



VOL. III. O 



