OF ARTS AND SCIENCES. 317 



Time in Velocity per 

 Seconds. Second. 



inches wide at top, and 2 inches high, with its edges 



turned towards the blast, as in the last experiment. Feet. 



gave very nearly the same results, .... 24.7 2.14 



" Exp. 11. A plate 2 inches wide at the base, 1.25 

 wide at the top, and 1.5 inches high ; angles of sides 

 with base equal to inclination of the plate with the 

 horizon, 76^ ; placed on the top of the fixed tube, on 

 the side next the blast, its base being raised .37 inch 

 above the mouth of the fixed tube, .... 29.5 1.80 



" A similar plate added to the opposite side of the 

 tube, 28.5 1.86 



" Similar plates on three sides ; open side from the 

 blast, 33.5 1.58 



" Similar plates on three sides ; open side at right 

 angle with direction of the blast, .... 32.2 1.65 



" Similar plates on four sides, .... 35.4 1.494 



" Exp. 12. Pyramid formed by the four plates, as 

 last arranged, with its base so fitted to the top of the 

 fixed tube that no air could enter by its side, . . 35.5 1.49 



" Exp. 13. Two similar plates, those used in the 

 last experiments, one arranged as in Exp. 10, and the 

 other similarly placed, but raised .37 inch above the 

 first, 29.0 1.83 



" The influence of the inclined plate, used in several of the preceding 

 experiments, would at once suggest the application of a figure of revo- 

 olution, which would have a similar effect upon the blast, that is, 

 would direct it upward, and thus assist the escape of the current from 

 the tube. A cone is evidently one form which would have this effect. 

 Indeed, the conical chimney-top has been long in use, and its principle 

 often reproduced under slight modifications of form. 



" The cone was proposed as a proper form for the chimney-top, and 

 an account of its application published, more than seventy years ago, 

 by Count Cisalpin, in a memoir entitled Description iVune Cheminee 

 et Etuve de Nouvelle Invention. The plan contrived by Cisalpin con- 

 sisted of truncated cones of plate or sheet iron, of different sizes. 

 ' When this apparatus is to be used,' says he, ' fit to your chimney 

 your first size ; it is of no consequence whether the chimney be round 



