S. Webber on Ventilation. 379 
which rose first will come round to the source of caloric, to receive 
afresh portion and-to rise again as before; and this. process will 
be repeated, till the whole of the air, if the room be. perfectly 
kept up, more or less active according to the greater or less con- 
ducting power of the walls. é “ 
But there will. not in any case be any permanent fixture of 
part of the. room will be the warmest 
If the calorific body possess also. the property of imparting 
The order of the process would be reversed if the aperture for 
occupied by warm and spent air. . If the word, spent be taken 
very literally, he may be considered as right, s, ent air so taken 
meaning air deprived of its power of sustaining life, which would 
be the ease with nitrogen; but-if, as the context would warrant, 
he meant-only air unfit to be breathed in consequence of having 
i Bes 
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