Yeans. NIV. AcwSez. _ 68 Dec. 19, 
If the process be continuous, and the proper amount of air be ad- 
mitted and removed every hour or minute, the only other requirements 
are that the entering air shall be pure, that it shall be properly warmed 
in cold weather, either before it enters the room or by the mixture and 
diffusion of wari and cold air in the room; and that the introduction 
and removal ot air shall take place by gentle or inappreciable currents 
in such a manuer that the pure air may be thoroughly diffused through- 
out the room before it is removed. 
These simple rules are easily sta'ed and comprehended. It is also 
well understood that to produce a movement of air requires force in 
proportion to the mass moved and the velocity imparted to it. 
The problems which arise in ventilation consist mainly in determining 
the position, arrangement and sizes of the passages through which the 
air enters and leives, and the proper adaptation of these passages to 
the forces which produce the movement. 
On the correct solution of these problems, too often misapplied or 
misunderstood, successful ventilation depends. 
The various modes of producing the movement of air for ventilation 
are: 
First.—Ventilating chimneys or flues in which the movement is 
caused by the difference in weight between the heated air in the flue 
and the cool-r air outside. This requires that the air before entering 
the flue shall be warmed, and the heat necessary may be that due to 
the heat of the room when fires are necessary for warmth ; or the heat 
may be imparted by stoves in the base of the flues, by gas jets, or by 
steam-heated pipes. 
Second.—The movement may be produced by fans or blowers or by 
steam jets - the latter being seldom applied. 
The object of this paper is to investigate the laws which govern the 
ventilation when the air is heated at the base of the flues by steam 
pipes, the air in its passage to the flue receiving heat by its contact with 
the exterior surface of the pipes. As far as I am informed these laws 
have not heretofore been developed, and, as this system is a very 
simple one, capable of very extended applications, it is hoped that the 
following analysis may at least lead to a full discussion of the subject : 
Let it be supposed that the air in a room is to be renewed at the 
rate of (W) lbs per second. Suppose also that it is to be rejected 
through a flue whose cross-section in square feet is (A), and height 
in feet (H). And that it is to be heated by steam coils whose aggregate 
exterior surface in square feet is (S) 
The following notations will be used : 
W. Weight of air removed per second (lbs). 
H. Height of flue in feet, 
