<S^ J^POGS IxJAV 267 



currents. These outer currents, being stronger, would force the foul an back, 

 down the flue. This would reverse the ventilating system, removing the 

 warmer, purer air instead of the colder, foul air. 



The old-fashioned wooden cupola was intended more as an ornament to 

 the barn rather than for the more practical purpose of aiding ventilation, 

 although in building it an attempt was made to keep out the weather. 



The wooden cupola, however, seriously interferes with the outflow of 

 air. Usually the total area of the outlet space between the louvres is less 

 than the cross section area of the flue, thus choking down the flow of air. 



Besides this interference with the air flow, the air currents, to escape, 

 must make a very sharp turn, as indicated by the arrows in Fig. 5. opposite 

 page, the flow of air almost turning back upon itself. 



Then, too, whirling or eddying currents are caused when the wind blows 

 into the cupola and comes into conflict with the upward current of warm air, 

 hindering still further the outflow of foul air. 



All together, these restrictions upon the free escape of the air make propei 

 ventilation impossible with the old-style wooden cupola. 



The ordinary, locally made metal cupola, is also unsatisfactory, not alone 

 because it is usually made far too small for the amount of foul air to be removed 

 but also because when made weatherproof, the cap must be placed too low, as 

 shown in Fig. 7, slowing down the outgoing current of air. Or if the cap is 

 placed high, the rain and snow and wind drive down the flue, as m Fig. 6. 



Both these types of cupolas shown in Figs. 6 and 7 have the fault present 

 in the wooden cupola — that of checking the outflow of air by having to make 

 a sharp turn and by the eddies created when the wind entering from outside 

 combats the upward flow of air in the flue. 



To prevent the troubles caused by the wind blowing into the flue, a storm 

 band is ordinarily used as shown in Figs. 8 and 9. This keeps out snow and 

 rain and makes the ventilator almost proof against the wind. 



In ventilators other than the James, however, the storm band hinders the 

 outflow of air by forcing the air current to make two sharp turns. 



Also, the upward current striking the top of the ventilator causes eddies, 

 choking the flue and interfering with the free escape of the foul air. A little 

 wind gets by the under side of the storm band and this, too, creates eddies. 



With the James Revolving Hood ventilator, however, the outgoing foul 

 air has a free outlet unimpeded by excess friction caused by right-angle turns, 

 by eddies or by being forced back upon itself. (See Fig. 10.) 



This is to a large degree true of the James Solid Hood Ventilator; up- 

 ward moving foul air strikes an upward sloping surface "A", Fig. 9, page 266. 

 In the James ventilator with revolving head upward sloping surfaces at "GG" 

 and "HH" (Fig. 10, page 266), turn the air gently outward and upward. 



This makes clear how, in James ventilators, offering the least possible 

 hindrance to outflowing foul air is used to increase the efficiency. 



