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“ Exp. 4. Elbow ; horizontal portion 4 inches long, opening turned from the blast, . . . . 70.0
“ Exp. 5. Same ; horizontal portion making, with the direction of the blast, an angle of 30°, . 46.0
“Same; angle of direction 45°, . .. 41.0
the blast, and having around its
“ Exp. 7. A perpendicular
“Same plate attached to the
“Same plate on the side of the fixed tube, opposite the blast, . . . . . no effect in 180.0
“ Exp. 8. A'square plate, 2 inches by the side, on the top of the fixed tube on the side next the blast, . 31.5 “Same plate making with horizon an angle of 80°, 28.2
" 75°, 27.3
70°, 29.0 67°, 28.7
66 22°, 65.0 “ Exp. 9. Square plate, 2 inches by the side, with vertical edges .5 inch wide, turned from the blast, and making an angle of 45° with its direction ; the whole plate making an angle of 75o with the horizon, 31.0
"Same plate, making same angle with the horizon, but with its edges turned in the opposite direction; that is, towards the blast, . . . . . 24.6
“ Exp. 10. A plate 1.25 inches wide at the base, 2
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, 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
“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 revoolution, 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 d'une Cheminée et Étuve de Nouvelle Invention. The plan contrived by Cisalpin consisted 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 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 accomplished, 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 Fig. 6.
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 Fig. 7.
being flat as in Cisalpin's, was also a truncated 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 Buildings, published in 1824, and still a standard work, refers to the conical
top as one which may often be employed with advantage, Fig. 8.
when formed in the manner described in fig. 8; and remarks, — 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 illustrated by figures, from one of which the annexed cut is copied. For its origin Mr. Tredgold refers to the memoir of De Lyle de Saint-Martin. It will be noticed
that the conical cap has, in the last figure, assumed the Fig. 9.
“ 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.
“ It is quite probable, that the conical and pyramidal earthen and brick chimney-tops now and for many years so generally used are modifications of those introduced or recommended by Cisalpin, SaintMartin, and Tredgold.
Time in Velocity per “ Exp. 14. A truncated cone, diameter of upper surface 1.25 inches ; diameter of lower surface 4.3 inches; height 1.3 inches ; lower surface upon fixed tube ; upper surface in centre of trunk, . . . 31.0 1.71
“ Exp. 15. Same cone divided into three cones of equal height by planes parallel to the two surfaces ; two smaller cones, . . . . . . 31.0 1.71
“ Smallest cone, . . . . . . 31.5 1.63
“ Exp. 16. Truncated cone, diameter of lower surface 2.1 inches; height .35 inch ; diameter of Aue anu upper suriace, as usual, 1.25 inches, . . 31.0 1.71
" Inclination of sides to base, in these last cones, the same ; 40°. Fig. 10.
“ Exp. 17. Cone; angle of side with base, at bottom 47°, at top 55°, side concave ; diameter of base, 3.7 inches ; height, 1.4 inches, . . . . . 35.4 1.49
“ Exp. 18. Cone ; angle of side with base, at bottom 44°, at top 64°, side concave; base 4 inches in diameter ; height 1.9 inches, 37.6 1.41
“ Exp. 19. Cone, with its cap, made according to the proportions laid down by Saint-Martin (see fig. 7),
“Exp. 20.* Cone and plate; inclination of sides to base 45°; diameter of base 2.9 inches ; height .83 inch (see fig. 9), . . . . . . .
* Dimensions of cone and plate, from which this model was made, as follow :- diameter of flue 18 inches ; base of cone 3ft. 6in.; height of cone 12in.; diameter of plate 3ft. 6in.; height of plate above top of cone Sin.; thickness of plate lfin.
Feet. 1.61 1.71
“ Exp. 21.* Cone and plate similar to last; base 2.5 inches in diameter; height.62 inch ; inclination of side to base 45° (see fig. 9), .. . . . . 33.0
“Same cone without plate, . . . . . 31.0
“ Exp. 22. Saint-Martin's cone without the cap; • to the upper surface and around the opening a hollow • truncated cone is fitted ; height .62 inch ; angle of sides 42° ; larger base of the frustum upward, . 24.0
“ Exp. 23. Cone used in Exp. 21, with a hollow truncated cone, .37 inch high, and angle of sides 42°, fitted as in last experiment, . . . . . 24.5
“ Exp. 24. Cone ; angle of sides with base 48° ; with hollow truncated cone, as in last experiment, . 25.0
« Exp. 25. Cone; diameter of lower base 2.5 inches ; diameter of upper base 1.6 inches ; height .55 inch ; internal diameter at lower base 1.25 inches, and diverging to 1.6 inches at upper base, . . 25.5
“ Exp. 26. Cone similar to that used in Exp. 21, with a flat plate, as recommended by Cisalpin (see fig. 6), .7 inch above top of cone; diameter equal to that of base of cone; on under surface of the plate a hollow cone .37 inch in height, lesser base downwards, 25.
0 “ Exp. 27. Square block representing a chimney ; flue 14 inches in diameter ; sides 2 inches; height 4 inches; one side towards the blast, . . . 33.5
“ Same, with corner towards the blast, . . . 35.5
“Same, with a small cone .5 inch high ; angle of side 63° ; side to the blast, . . . . . 37.5
“ Exp. 28. Same block, with its plane upper surface inclined towards the blast, at an angle of 3° with the horizon, . . . . . . . . 37.0 “ Same, at an angle of 10° with horizon, . . 39.0
" " " 200 " . 87.0
1.43 1.36 0.609
* Dimensions of the original of this model : - diameter of flue 8 inches; diameter of cone at base 16 inches; height 4 inches; diameter of plate 16 inches, and 4 inches above top of cone.