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PROCEEDINGS OF THE AMERICAN ACADEMY 



Fisr. 6. 



or square, provided it have no holes in its sides, and is open only at 

 the top ; if this put a stop to the smoking, your object is probably ac- 

 complished, the equilibrium between the wind and smoke is destroyed 

 (nevertheless assure yourself of this by many experiments, made at 

 different times), and then you have nothing further to 

 do than to attach to three sides of the cone three 

 rods of iron, four, five, or six inches long, on which 

 place horizontally a round plate, having a diameter a 

 little larger than that of the cone, to prevent the 

 rain from entering the chimney.' The adjoining 

 figure is an elevation from the perspective view 

 given in the memoir. 

 " In 1788, De Lyle de Saint-Martin, a lieutenant in the French 

 navy, again called attention to this form of chimney-top, in a memoir, 

 giving a full description, with drawings, of its construction, and the 

 results of his experiments. The cap surmounting the cone, instead of 



being flat as in Cisalpin's, was also a trun- 

 cated cone, but differing in its proportions 

 from that forming the chimney-top. This 

 arrangement, which is here figured from 

 Saint Martin's memoir, was examined and 

 approved by the French Academy of Sciences, 

 and published in its Transactions. 

 " Mr. Tredgold, in his treatise on Warming and Ventilating Build- 

 ings, published in 1824, and still a standard work, refers to the conical 

 top as one which may often be employed with advantage, 

 when formed in the manner described in fig. 8 ; and re- 

 marks, — ' The upper cap prevents down blasts of air, but 

 in a steady horizontal wind the lower cone alone would 

 be sufficient.' Its mode of action is described and il- 

 lustrated by figures, from one of which the annexed cut 

 is copied. For its origin Mr, Tredgold refers to the me- 

 moir of De Lyle de Saint-Martin. It will be noticed 

 that the conical cap has, in the last figure, assumed the 

 spherical form. 



" The annexed cut shows the same truncated cone, 

 which has, during the past year, been introduced as quite 

 a novelty, the inventor having gone back to first princi- 

 ples, and again mounted the flat top. 



