CHAP. I. 



COVERED YARDS. 



665 



is known as u roof ventilation " (in contradistinction to " wall ventila- 

 tion," which allows a free current of air to enter the yard over low end 

 or side walls at a height little above that of the animals kept in it), and 

 was invented by Sir Harry Meysey Thompson. The materials formerly 



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a 



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used for roof-cover and cattle yards were slates and pantiles. The 

 latter have been very extensively employed, and are less susceptible 

 than slates to changes of temperature. More recently corrugated iron 

 and boards have come into use, and, to some extent, felt and Willesden 

 paper. 



