232 On Warming and Ventilating 



a number of lights, would, under such an arrangement, soon 

 render the air unfit to breathe. Hence will appear the necessity for 

 two currents into a room. The inlet for fresh air should be in a 

 situation not liable to annoy those sitting in the room ; the outlet 

 is generally provided for in the chimney, which is commonly suf- 

 ficient for rooms of ordinary size, but is mostly too small for 

 large public rooms. 



It will be evident from what has been observed, that in order 

 to render rooms comfortable and wholesome, two objects are 

 required. The one is, to keep up an uniform and agreeable tempe- 

 rature ; the other to provide for a change of the air sufficient to 

 preserve that degree of purity essential to health, and which per- 

 sons under certain pulmonary affections can so nicely appreciate. 



It is evident that the former of these objects can never be at- 

 tained by radiant heat ; and yet, an open fire, which scarcely 

 affords any other than radiant heat, is so connected with our 

 domestic habits that it will be very long before the open grate 

 will be entirely set aside. Under these circumstances, it has 

 been found most expedient to use the combined eflect of radiant 

 heat with a constant supply of fresh air, raised to an agreeable 

 temperature in the winter ; and which, in certain cases may be 

 cooled during the excessive heat of summer. 



Great difficulties have been experienced in most of the means 

 hitherto employed for warming air. In the first place, from what 

 has been previously observed concerning the action of the solar 

 rays on the earth, the air cannot be warmed by radiant heat 

 passing through it ; therefore we can only give heat to a trans- 

 parent fluid by bringing its particles in contact with a heated 

 surface, and, in proportion as elastic fluids are more expansible, 

 they are heated with more difficulty. 



There are a number of properties which a body should 

 possess, to afford a surface proper for heating air intended to 

 warm and ventilate rooms. For the sake of economy it should 

 be a good conductor of heat, in order that the radiant heat which 

 it receives on one surface may be freely transmitted to the other. 

 The surface to be heated should be clean, that is, free from 

 any foreign matter, but not polished ; and when the temperature 



