116 BOARD OF AGRICULTURE. [Pub. Doc. 



extent when it comes in contact with it that it no longer 

 continues to rise, but again falls to the floor. The cooled 

 air in the upper part of the building acts as a cushion, against 

 which the rising current strikes. 



The second force of natural ventilation is that of the diffu- 

 sion of gases. This force acts upon gases overcoming the 

 force of gravitation. The heavier gas rises, the lighter 

 descends. In stable ventilation this force acts to prevent the 

 heavier gases from displacing the lighter ones. Otherwise, 

 the heavier gases would form in layers above the floor in 

 order of their specific gravities. The heavy, poisonous car- 

 bon dioxide (CO.^), exhaled from the lungs, would, in a 

 close, tight-walled stable, continue to collect upon the floor, 

 until the animals might become completely surrounded by it. 

 We might have the same condition in our stables as is fre- 

 quently seen in deep wells or mines, — a collection of CO2 to 

 such an extent that death results when a person descends 

 into them, unless the gas has been previously forced out by 

 means of fans, as in mine ventilation, or by means of a bundle 

 of burning straw which is let down into the well to create an 

 upward current and produce sufiicient circulation to remove 

 the carbon dioxide. 



The tendency of gases to diffuse is so great that they will 

 readily [jass through walls of brick or wood that have not 

 been rendered impervious by the application of paint or 

 paper. When a wall is constructed of a single thickness of 

 straight-edged or matched boards, air will readily difluse 

 through the cracks and crevices ; but when sheathing paper 

 and clapboards, particularly the former, are used over rough 

 boarding, the process of diffusion is arrested. 



The great advantage of the modern method of construction 

 over the old is that we have conditions which are more under 

 our control. The quantity of air brought in and removed 

 can be varied to suit conditions of the weather and tempera- 

 ture outside. 



The most important force of the natural system of venti- 

 lation to be considered is that of the wind. It is a strong 

 ventilating agent, and the only one that need be taken into 

 account in connection with mathematical calculations relative 

 to the subject. Its irregularity of action constitutes its 



