CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This instrument, filed under 37 CFR 1.53(b) and 1.78 invoking the provisions of 35 U.S.C. 120, is a Continuation in Part of presently copending application Ser. No. 11/492,232 entitled “High Wind Bio-Mass Cap”, filed Jul. 25, 2006. 
     
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
       [0002]    Not Applicable 
       THE NAMES OF THE PARTIES TO A JOINT RESEARCH AGREEMENT 
       [0003]    Not Applicable 
       INCORPORATION-BY-REFERENCE OF MATERIAL SUBMITTED ON A COMPACT DISC 
       [0004]    Not Applicable 
       BACKGROUND OF THE INVENTION 
       [0005]    1. Field of the Invention 
         [0006]    Chimney Draft Systems; Emission Ducts 
         [0007]    2. Description of Related Art 
         [0008]    Occasionally a descriptive term in this application may be shortened so as to recite only a part rather than the entirety thereof as a matter of convenience or to avoid needless redundancy. In instances in which that is done, applicant intends that the same meaning be afforded each manner of expression. Thus, the term first canopy venting leaf ( 11 ) might be used in one instance but in another, if meaning is otherwise clear from context, expression might be shortened to venting leaf ( 11 ) or merely leaf ( 11 ). Any of those forms is intended to convey the same meaning. 
         [0009]    The term attach or fasten or any of their forms when so used means that the juncture is of a more or less permanent nature, such as might be accomplished by nails, screws, welds or adhesives. Thus it is stated herein that in many instances, both canopies ( 1 ,  2 ) are respectively attached to the assembly&#39;s collar ( 3 ). A connection in which an object would be easily removed from another is described by the word emplace as where it is stated that preferably, where both ( 3 ,  400 ) are cylindrically shaped, the collar ( 3 ) is emplaced upon a smokestack ( 400 ). Employment of the words connector join or any of their forms is intended to include the meaning of any of those terms in a more general way. 
         [0010]    The word comprise may be construed in any one of three ways herein. A term used to describe a given object is said to comprise it, thereby characterizing it with what could be considered two-way equivalency in meaning for the term. Thus, it is stated that the subject matter hereof comprises an assembly featuring a specially shaped venting assembly, meaning that the latter is in fact the former and the former, the latter. The term comprise may also be characterized by what might be considered one-way equivalency, as when it is stated herein that preferably, welds comprise the leaf-to-collar attachment means ( 34 ). This use of the word has a generic sense to it. That is, a weld will always be leaf-to-collar attachment means ( 34 ) but leaf-to-collar attachment means ( 34 ) may be a weld in one case but something else-nuts and bolts, for instance—in another. However, the word comprise may also be used to describe a feature which is part of the structure or composition of a given object. Thus, it is said the collar ( 3 ) comprises diameter sufficient for axial connection to the smokestack ( 400 ). The meaning in the respective cases is clear from context, however. Accordingly, modifying words to clarify which of the three uses is the intended one seem unnecessary. 
         [0011]    Terms relating to physical orientation such as top or bottom, upper or lower, upwards or downwards, refer to the positioning of an object in the manner in which it would be typically oriented for use or viewing. Assemblies of the sort addressed herein are positioned at the top of the smokestack ( 400 ), the first vent canopy ( 1 ) is spoken of as the uppermost one and the venting leaves ( 11 ,  21 ) are connected to the collar ( 3 ) at their ( 11 ,  21 ) lower and outer ends. References to airfoil surfaces herein, ante, also share these descriptive characteristics. These terms of orientation should be interpreted to represent respective aspects or dispositions of members of the assembly in a consistent manner—even if it were, for example, held upside down in certain instances. 
         [0012]    The term axially disposed as used herein denotes a relationship between a point of reference upon a first object with a second configured so as to comprise an axis wherein the first&#39;s point of reference is lined up or aligned with the axis of the second. The assembly is, thus, said to be axially disposed upon a smokestack ( 400 ) and the assembly&#39;s collar ( 3 ), beneath the respective vent canopies ( 1 ,  2 ). 
         [0013]    Chimney caps of one configuration or another have been with us for some time. It is probably fair to say that all of them have provided some degree of usefulness wherein the focus has generally been upon keeping rain out of the chimney while allowing the rising smoke to escape. Less attention was paid to enhancing the passage of air through the vents so as to provide a proper smoke draw but even that has not been completely overlooked. The science of gas emission through orifices, pores or suitably designed openings in general has only reached the stage—so to speak—this past 25 years or so. Engineers, having observed the efficiency with which oxygen-carbon dioxide exchange occurs through exquisitely formed stomata of leaves borrowed from nature in some instances. Just the right size or shape of opening permits the sought-after optimum level of performance. It is certainly true, for example, that kitchen gas ranges have benefitted from that enterprise. Numerous industrial applications along that line undoubtedly exist 
         [0014]    There is a distinction relative to the application of a chimney or smokestack ( 400 ) venting system. Furnace, wood stove or fireplace arrangements which heat ambient air within the structure to be heated and then pass the burned byproduct or smoke up the stack ( 400 ) to the outside are identified as one-way heating systems. Those which admit air from the outside into the heating chamber, heat it and thereby warm the interior of the structure—adding it to the ambient air, as it were—and then, like the other, pass the smoke upward to the outside are two-way heating systems. The distinction is important in designing what is positioned atop the chimney or smokestack ( 400 ). Two-way systems entail a more complicated design because they must assure the incoming air does not interfere with that which is outgoing and vice-versa. Ventilating systems dedicated to simplicity—particularly those which are configured to accommodate the passing wind in a particular way—are most properly constructed for one-way heating arrangements only. 
         [0015]    Long now in the public domain is U.S. Pat. No. 538,366 issued to Cooper, comprising a four-piece assembly of bent sheet metal to create a crown attached to the chimney or smokestack( 400 ) top. Following along, U.S. Pat. No. 4,103,600 issued to Bridge provided a simple partially overlapping arrangement of two bent wide strips of metal positioned with respect to one another to permit a somewhat isolated passage for smoke therethrough. Even before the Bridge assembly, however, U.S. Pat. No. 3,826,181 issued to Schrade addressed the benefits of what he called “optimum aerodynamic performance” wherein a partial vacuum accommodated the wind-flow. The Schrade assembly comprised two crown systems—outer and inner—in each of which two bent strips interconnected to provide domed structures connected to the smokestack ( 400 ) at their lower outer ends. The crown systems were radially alternated with reference to one another so that the passage of air therethrough was convoluted to some degree; thus contributing to the aerodynamically efficient feature of the assembly, now extant for more than 30 years. U.S. Pat. No. 4,325,291 issued to Paynton, et al also exhibited that configuration in general, appearing to encompass the workable features of Schrade. Both employ the radially disposed alternation referred to supra, and as an incidental matter, both also confer a hinged character upon one of the strips so that it can be lifted up for access into the interior. 
         [0016]    One might be tempted to think that little can be done in the way of revision to improve those designs. Not so, however, experience has demonstrated that systems employing not merely two but three or more intersecting venting leaves in each of two generally concentric canopies work substantially better than merely two of them to provide a much enhanced Bernoulli effect with the passing wind. 
         [0017]    The reason for improved emission in specially configured assemblies is most properly attributed to what has been identified as the Bernoulli effect wherein, for a specially shaped object moving through the air or situated so as to permit the passage of moving air ( 601 ) over it such that relative motion was along an airflow vector ( 600 ). The motion was observed to create a partial vacuum at a point of relative discontinuity—such as the upper declining curve of an airfoil ( 500 ). In aircraft, this partial vacuum site—referred to herein as a sector of lower pressure ( 620 )—was observed in conjunction with what is referred to herein as a sector of higher pressure ( 610 ) beneath the airfoil ( 500 ) to provide an upward force vector ( 700 ) providing what was generally recognized as “lift”, such that the forward moving aircraft remained in the air. To explain, it was seen the moving air ( 601 ), separating over the top and bottom of the airfoil ( 500 ) took two paths to rejoin at a posterior point—that is, the respective bulks of separated air ( 601 ) necessarily merged with one another to continue the stream. That air ( 601 ) moving over the curved surface of the airfoil ( 500 ) required a longer path and, thus, moved faster than the air ( 601 ) passing along the relatively straightened surface of the airfoil&#39;s ( 500 ) underside—the sector of higher pressure ( 610 ) addressed supra. The greater velocity of the uppermost air( 601 ) provided the partial vacuum. Essentially the same effect was later demonstrated by Venturi wherein the air ( 601 ) passing through a constriction in a tubular pathway was observed to accelerate, creating—as expected—the partial vacuum. 
         [0018]    While the prior art has made some strides along the foregoing lines, certain performance improving configurations yet remain to be provided to fulfill the expectations of the avid exerciser. 
       BRIEF SUMMARY OF THE INVENTION 
       [0019]    A crown-like assembly is shaped to sit atop a chimney flue or smokestack such that the rising smoke from a heating system or fireplace below enters its underside. Emission of the smoke is aided by the passage of wind though openings in the crown. 
         [0020]    The crown comprises a first—or outer—canopy ( 1 ) and as well as an inner one ( 2 ) disposed so that the first ( 1 ) envelopes the second ( 2 ). The two ( 1 ,  2 ) are separated somewhat to allow the wind to pass through. Each canopy ( 1 ,  2 ) comprises a number of strips curved, bent and joined generally at their centers to form the uppermost part of the crown and fastened downwards at their ends to a ring-like collar ( 3 ) which fits over the smokestack ( 400 ). It is, of course, this curved bent configuration which provides the crown-like appearance. 
         [0021]    Thus, the second—or inner—canopy is contained within the first—or outer—canopy, each with the strips—or venting leaves ( 11 ,  21 ), as identified herein—so arranged as to provide partially diverted and divided pathways for the entering wind. Most importantly, the disposition, number, size and configuration of the leaves ( 11 ,  21 ) is such as to increase the velocity of the air or wind therein, creating the desired Bernoulli effect, supra. So constructed and emplaced, the assembly enhances considerably the emission of the smoke from and, in turn, that of the combustion of, the burning system below. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         [0022]    Solid lines in the drawings represent the invention. Dashed lines represent either non-inventive material, that not incorporated into an inventive combination hereof and which may be the subject of another invention, or that which although so incorporated, lies beyond the focus of attention. 
           [0023]      FIG. 1  is a perspective view of a version of the Bernoulli effect smoke draft vent assembly wherein both canopies ( 1 ,  2 ) comprise bolts and nuts as interleaf attachment means ( 14 ,  24 ). 
           [0024]      FIG. 2  depicts an exploded view of the assembly 
           [0025]      FIG. 3  illustrates an exploded view of a vent canopy variant—in this case, of the first ( 1 ), although actually representative of either ( 1 ,  2 ). 
           [0026]      FIGS. 4 and 5  represent overhead views, respectively, of the first and second vent canopies ( 1 ,  2 ). 
           [0027]      FIG. 6  demonstrates the Bernoulli effect upon an airfoil ( 500 ), exhibiting airflow ( 601 ) and the associated vectors ( 600 ). 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0028]    The subject matter hereof comprises an assembly featuring a specially shaped venting structure designed to sit atop the smokestack ( 400 ) of a fireplace or the like. It is intended to work not as a two-way venting system but only as a one-way one, supra. 
         [0029]    The overall assembly adopts the benefits of the Bernoulli effect, comprising a pair of vent canopies ( 1 ,  2 )—a first vent canopy ( 1 ) and a second thereof ( 2 ). Each ( 1 ,  2 ) comprises three or more venting leaves ( 11 ,  21 , respectively) which are disposed to cross one another ( 11 ,  21 ) proximate their centers. Preferably, the leaves ( 11 ,  21 ) as members of each set thereof ( 11 ,  21 , respectively) are fastened together at that site—that is, the members of the set of first canopy venting leaves ( 11 ) would be joined to one another( 11 ) and those of the second canopy set ( 21 ), respectively, to one another ( 21 ). The connections for those ( 11 ) of the first canopy ( 1 ) are made by first canopy interleaf attachment means ( 14 ) and those ( 21 ) of the second canopy ( 2 ), by second canopy interleaf attachment means ( 24 ). Attachment means ( 14 ,  24 , respectively) may comprise merely bolts and nuts. 
         [0030]    Both canopies ( 1 ,  2 ) become attached to a collar ( 3 ) also comprised by the assembly. To that end, each venting leaf ( 11 ,  21 ) comprises at its ends ( 11 ,  22 , respectively) an embracing flange ( 12 ,  22 ). The venting leaves ( 11 ,  21 ) are disposed to curve downward so that the embracing flanges may be attached to the collar ( 3 ) by suitable leaf-to-collar attachment means ( 34 ). 
         [0031]    The attachment means ( 34 ) may comprise nuts and bolts fastened through attachment orifices ( 35 ) disposed in the flanges ( 11 ,  21 ). It is preferred welds comprise the means ( 34 ), however. 
         [0032]    The arrangement of the canopies ( 1 ,  2 ) is such that the first is positioned a short distance—usually an inch or two—above the second so that the flow of air between them ( 1 ,  2 ) is not impeded. The amount of spacial separation may depend, of course, upon the assembly&#39;s size. It may, therefore, be properly stated in shorthand parlance that the first vent canopy ( 1 ) is disposed to overlie the second ( 2 ) in separation therefrom ( 2 ). 
         [0033]    In most arrangements, the smokestack or chimney flue ( 400 ) upon which the collar ( 3 ) is connected is cylindrically shaped, although other cross-sectional configurations may be extant. In most cases, therefore, the collar ( 3 ) will also be cylindrically shaped for its ( 3 ) proper connection to the smokestack ( 400 ). It is conceivable that a collar ( 3 ) may be disposed in some manner upon a smokestack ( 400 ) of non-matching configuration. Certainly, the preferred arrangement entails emplacement or other connection of a cylindrically shaped collar ( 3 ) upon a cylindrically shaped smokestack ( 400 ). A number of ways to accomplish this are known. Where acceptable, the collar may be configured with an internally disposed shoulder to allow it to be slipped into place around the exterior of the smokestack ( 400 ). In many instances, emplacement of that sort may meet all of the needs considered. However, if desired, attachment may be adopted for connection. In any event, it is appropriate to state that the collar ( 400 ) comprise diameter sufficient for axial connection upon a smokestack ( 400 ). 
         [0034]    In attaching the venting leaves ( 11 ,  22 ) to the collar ( 400 ), it is preferred those ( 21 ) of the second canopy ( 2 )—necessarily the smaller of the two ( 1 ,  2 ) by reason of its ( 2 ) disposition below and, therefore, within the encompassing first canopy ( 1 )—be set in place before attaching those ( 11 ) of the first ( 1 ). Attachment arrangement of the respective embracing flanges ( 12 ,  22 ) may, of course, be made upon the collar ( 3 ) in any convenient manner and at any selected site, so long as spaces for air passage are left between the curved venting leaves ( 11 ,  21 ). However, it is preferred by far that the second canopy&#39;s embracing flanges ( 22 ) be spaced around the collar ( 3 ) to allow room for those ( 12 ) of the uppermost first canopy ( 1 ) disposing the attachment points of the embracing flanges in an alternate fastening arrangement. Thus, the flanges ( 21 ,  22 ) would encircle the collar ( 3 ) in every-other fashion—a second canopy flange ( 22 ); then, a first canopy flange ( 12 ); a second canopy flange ( 22 ) again; next, another first canopy flange ( 12 ); and so on. Experience has demonstrated that, so long as not less than three venting leaves ( 11 ,  21 ) for each canopy ( 1 ,  2 ) are incorporated within the assembly, this preferred arrangement, herein designated one of angular offset array, to be one providing an improved airflow through the leaves ( 11 ,  21 ). It may, thus, be said as a matter of preference that by reason of the relative attachment sites of the venting leaves ( 11 ,  21 ) upon the collar ( 4 ), those ( 11 ) of the first canopy ( 1 ) be disposed in angular offset array from those ( 21 ) of the second canopy ( 2 ). 
         [0035]    To take matter a step further, however, it is even more acceptable if all-around spacing of the attachment sites be even instead of irregular. It would, therefore, be stated as a matter of greater preference that the central angle between each pair of adjoining venting leaves ( 11 ,  21 ) equals that between each other pair thereof ( 11 ,  21 ) and that the angular offset array of the first canopy&#39;s venting leaves ( 11 ) with respect to those ( 21 ) of the second ( 2 ) be regular such that each first canopy venting leaf ( 11 ) bisects the central angle between a pair of adjoining venting leaves ( 21 ) of the second canopy ( 2 ). 
         [0036]    By reason of the common attachment site of the embracing flanges around the collar ( 400 ), it necessarily follows that the collar ( 400 ) occupies—at least in approximation—a centered position vis-a-vis the canopies ( 1 ,  2 ) and it may, therefore, be properly stated that the collar ( 400 ) is axially disposed below the vent canopies ( 1 ,  2 ). 
         [0037]    Because the first vent canopy ( 1 ) overlies and more or less envelopes the second ( 2 ) in relative configuration, its leaves ( 11 ) are obviously longer than those ( 21 ) of the second ( 2 ). While it is not essential the venting leaves ( 11 ,  21 ) of the respective canopies ( 1 ,  2 ) be equal in length—that is, for all of the first canopy&#39;s leaves ( 11 ) to comprise equal length with respect to each other ( 11 ) and all those ( 21 ) of the second canopy&#39; ( 2 ) to so comprise, it is again more acceptable for such to be the case. It would, therefore, be properly stated as another matter of preference that the venting leaves ( 11 ,  21 ) of the respective vent canopies ( 1 ,  2 ) be equal in length to one another ( 11 ,  21 , respectively). 
         [0038]    The disposition of three sets of venting leaves ( 11 ,  21 ) for each canopy ( 1 ,  2 ) in the manner presented herein, supra, provides a highly efficient Bernoulli effect draft vent for the exiting smoke. Applicant is as yet unaware of the reason why such sets of three—as opposed to a lesser number—provide those results. Each of the sets of three provide three paired side-by-side openings. Although it is a matter of speculation, the diversion of wind entering a given pair of the three sectors to one side and the other—the right and left—through the remaining two pairs thereof may provide just the optimum Bernoulli effect velocity to accomplish the assembly&#39;s intended purpose. As thus far observed, assemblies with three such sets of leaves ( 11 ,  21 ) are also even preferred over a greater number thereof ( 11 ,  21 ) and undoubtedly more economical to manufacture.
A crown-like structure sits atop a chimney or smokestack as a specially formed chimney cap wherein passing air is required to take a somewhat convoluted path, providing a Bernoulli effect to improve smoke emission draft. Like at least two of its predecessors, the crown has two roof-like canopies, one within the other, each having a series of curved, bent strips separated to permit the wind-flow to pass through. As a departure from the past, the number of sets of strips, or leaves, within each canopy is raised to optimize performance, the preferred number thereof being three.