382 SS. Webber on Ventilation. 
warm air will occupy the centre of the flue, and the descending 
current of cool be distributed around its sides. In a room other- 
wise close, such ventilation would be very imperfect, as the ac- 
tion of. cold external air on whatever part of the chimney was 
exposed to it, would be constantly counteracting the effects on 
the chimney of the ascending current of warm air within, by 
abstracting the caloric it imparted, and thus prolonging the strug- 
gle between the ascending and descending currents, and with the 
assistance, when the wind was high, of the pressure of a strong 
current of air above the opening: of the chimney, preventing the: 
warm air from rising freely into the atmosphere, and_ possibly 
occasionally eddying downwards into the flue, it would frequently 
eceed in forcing the ascending current back into the room. 
Hence many chimneys smoke badly in very cold and windy 
weather, that in calm and mild weather convey smoke readily, 
hence a very hot fire is in stich cases the most appropriate 
remedy, as giving sufficient force to. the ascending current to 
overcome these obstacles. / é 
But. still in order that a fire may burn freely, and warm and 
impure air escape readily through a chimney, jt is necessary that 
some supply of fresh and cooler air should have admission toa 
room through some other opening than the chimney, so as t 
leave that free for the ascent of the warm air, since if such an 
admission ean be made below, this ascending current will soon 
fill the whole of the flue without material obstruction. — - 
~The usual and almost:necessary inaccuracy of the joinings of 
doors and windows generally supply sufficient air for this purpose, 
but the cold drafts which they occasion are at least disagreeable, 
and often hurtful, and in cold countries, efforts are made to close 
these openings effectually by means of double windows and 
doors, listings, &c. In proportion however as these succeed 
the impurity of the,air and the difficulty of making the fire burn 
increase, and some remedy for these is necessary. No remedy 
seems better than that recommended by Professor Hosking, but 
as was shown in: the beginning of this article very long 8 
brought forward and practised by others, namely, the introduc 
tion into the room of fresh air sufficiently heated -at least pot 0 
chill the room, and if necessary to assist in warming it or 10 
warm it wholly.» . ‘ ; 
But if we understand Professor Hosking’s statement aright, i 
accidental and unavoidable chinks and cracks, Now if the: 
