2 HOW TO BUILD A CHIMNEY. 
way up. So much for the vent. A very important 
matter, however, is its mouth or entrance. When it 
is desired to direct the flow of a wide stream into a 
narrow channel, the channel is made wide at the 
mouth and gradually narrowing to the narrow chan- 
nel. So, to direct the current of smoke into the nar- 
row vent, the mouth of the vent must widen, so as 
to enclose all the smoke, and gradually narrow. All 
sharp shoulders must be avoided. The vent must be 
like an inverted funnel, or like a helmet hat, with 
the crown elongated and open to form the vent. 
There is no advantage gained, and much heat lost, 
by having the chimney and fire far back into the 
wall. If the front edge of the funnel rim (or hat 
brim) comes far enough forward to catch all the smoke, 
no more is needed. If the lintel ofthe fire-place 
were the chop of an old pulper, its edge forming the 
rim of the funnel, and the vent gradually narrowing 
from that upwards, one foot and a half would be far 
enough back for the wall behind, and the fire would 
thus give out plenty of heat, and all the smoke go 
up the vent. | 
Suppose the dimensions as follows :— 
ire-place, width 24 feet, from back to front 14 
foot, height of lintel 3 feet, chimney vent 80 inches. 
square, or 10x 8. 
Fire-place, width 2 feet 9 inches, back to front 1 
foot 8 inches, height of lintel 3 feet 6 inches, chim- 
ney vent 120 inches, or 12x 10. 
The fire-place should be so constructed that the air 
may get freely wnder the centre of the fire, but not 
behind it, otherwise the current rushing in behind fills 
up the chimney, and forces the smoke forward, and 
out into the room. A very simple way of avoiding 
this is to make the bars reach only half-way back, 
closing up the space behind, or, if bricks only are 
used, leaving an open ho'e, say the space of a brick, 
half-way, i.e., nine inches in from the front. The 
current of air thus getting in below the fire, and being 
directed upwards through its centre, carries the smoke 
upwards and backwards safely into the vent. 
Another thing of importance is the chimney-top: 
aif there were no wind or rain, it would only be ne- 
cessary to leave it open the same width as the ehim-. 
ney. As there is wind, however, and that generally 
so very much stronger in cnrrent than the current 
of smoke, as to beable to stop it, and turn it back, 
it must be guarded against. Where the wind is blow- 
ing level there is little difficulty. A little contraction 
at the top, such as the pressure, &c., will bear, may 
give speed to the smoke current, to push through the 
horizontal wind current. Where the wind current 
