TEANSPORT BY SEA AND LAND 903 



mouthed cowls, communicating with air shafts, which ex- 

 tend fore and aft along each side or midships. The shafts 

 have perforations at every five or six feet. 



If used for extracting foul air the ventilator is turned 

 from the wind, a steam cock which passes into the interior 

 of the ventilator is opened, and the steam thus ejected 

 passes through a jetting arrangement and creates a vacuum, 

 by which means foul air is drawn off while fresh air enters 

 through the hatchways. 



A 16-inch main ventilator with the steam on will extract 

 60,000 cubic feet of air per hour, which is a mere trifle 

 where horses are concerned. As an air inlet it is turned 

 towards the wind, the steam is cut off and air is driven 

 along the shafts which are in communication with it. 



Edmonds' system may be found on many transports; it 

 is imperfect, but better than nothing. 



We have previously dealt (p. 74) with the loss caused 

 by friction in a tube or by bends. These are the difficulties 

 and losses experienced by driving air through any tube 

 system on a ship. As seen earlier in these pages a circular 

 tube is preferable to any other shape, and should always be 

 employed where possible. Of the various methods men- 

 tioned above, none would appear to be more likely to be 

 effective than that of jets of compressed air; it is known as 

 Green's system. A cubic foot of air under a pressure of 

 3 lbs. or 4 lbs. to the inch, is said to induce the extraction 

 or propulsion of 25 cubic feet of ordinary air. 



No ships for animal transport that we know of are 

 ventilated artificially, with the exception of Edmonds' 

 steam jet, but some such system is what has to be adopted 

 on a man-of-war. The latter class of vessel, in the matter 

 of ventilation, is in much the same plight as the main and 

 lower deck of an animal transport. 



It is obvious that all the decks of a horse or cattle ship 

 are not equally foul ; the lower we go in the interior of a 

 ship the more difficult ventilation becomes, though strange 

 to say it is the main and not the lower deck which furnishes 

 the greatest amount of sickness. This is accounted for, 



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