230 



PNEUMATICS. 



Fig. 191. 



Fig. 190. regarded as incurable. Fig. 190 



is intended to show the mode of 

 its operation, the wind, as shown 

 by the arrows, being deflected for 

 a considerable distance on the lee 

 side, so as to form a vacancy at 

 a, which the wind from the other end and from the 

 chimney both rush in to supply. Being fixed on with- 

 out turning in the chimney, it is both simpler and less 

 noisy than any caps furnished with a vane. 



EmersoTi's Chimney-cap, lately invented, is differ- 

 ent in construction, but quite similar in 

 principle to the preceding. It is shown 

 by Fig. 191. A sheet-iron pipe is set in 

 the top of the chimney, furnished with 

 the conical rim, and a plate or fender 

 on the top which excludes the rain. Be- 

 tween the plate and rim is a space 



Fig. 192. 



quite simi- 

 lar in form or section to 

 that represented by Fig. 

 190. 



In exposed situations, 

 chimneys are found to 

 draw more imiformly by 

 contracting the top about 

 a third less than the rest 

 of the flue. The current 

 at the moment of escape 

 is swifter than below, and 

 less acted upon by any 

 downward check from the 



