referring now to the drawing , fig1 depicts a sawdust pile 20 which , as indicated above , may be upwards of fifty feet high , seventy - five feet wide at the base , and several hundred feet long . sawdust is dumped onto pile 20 or in the area 22 in which the pile is located from a horizontal , overhead conveyor 24 of conventional construction which extends the length of the sawdust pile . conveyor 24 is encased in a u - shaped housing 26 which is open at the bottom and is known as a &# 34 ; mailbox &# 34 ;. the conveyor includes an upper run 28 and a lower run ( not shown ) supported by a structural framework 30 . the conveyor is mounted at the elevated position shown in fig1 on ladder - type supports 32 of conventional construction . associated with conveyor 24 is an equally conventional tripper 34 which is designed to traverse the length of the conveyor and to dump material from the latter onto pile 20 or into area 22 at designated locations therealong . particulate material is removed from the bottom of pile 20 by a combination of augers 35 ( only one of which is shown ) and endless conveyors 36 . both the endless conveyors and augers are conventional . the latter extend crosswise of pile 20 and are mounted so that they can traverse the length of the pile . this allows particulate material to be recovered from the latter at any designated location therealong . as those skilled in the relevant arts will appreciate from fig1 augers 35 transfer the particulate material to the center of pile 20 and onto conveyors 36 which , in turn , convey that material to the end of , or beyond , pile 20 . the endless conveyors are housed in a vault 38 having a roof 40 that is designed to keep the particulate material from cascading into the vault . as suggested above , pile 20 and the equipment employed to form that pile and remove particulate materials from it are of conventional character . accordingly , neither the characteristics of the pile nor the details of the materials handling equipment will be described further herein except as is necessary to an understanding of the present invention . as far as that invention is concerned , it will be obvious to the reader from fig1 that wind can entrain and scatter material being dumped onto the pile from conveyor 24 at the location determined by tripper 34 and , similarly , pick up loose material from pile 20 and scatter it . the resulting environmental pollution is currently considered sufficiently serious to warrant sanctions as high as $ 10 , 000 per day for installations found to be in violation of current regulations . referring now to fig2 , and 5 , pollution of the environment with particulate material is prevented in accord with the principles of the present invention by suspending a platelike windfoil 42 between overhead conveyor 24 and the top 44 of the pile 20 of sawdust or other particulate material . in one typical application of the present invention windfoil 42 is fabricated from a three - eighths inch thick steel plate and has a height of sixteen feet . the windfoil spans between one - fourth and one - fifth of pile 20 and is fabricated in multiple , eight foot long sections 45 as shown in fig3 . protecting even this relatively small fraction of pile 20 against erosion with a windfoil was found to be effective . as indicated above , major pollution problems occur when material is being dumped on a pile such as that shown in the drawing . consequently , by dumping on the protected part of the pile under windy conditions and on the remainder only when the air is calm , entrainment of particulate solids in the air surrounding the pile and the consequent environment pollution can be prevented . the operation of windfoil 42 can best be appreciated from a comparison of fig4 and 5 . absent the windfoil , cross winds flow through what is in effect a venturi between conveyor 24 and pile 20 as shown by flow lines 46 in fig4 . the wind picks up particulate material being dumped onto the pile from the conveyor and , also , strips particulate material from the pile . the problem is pronounced because of the high velocity imparted to the wind because of the just discussed venturi effect . in contrast , with windfoil 42 installed , wind blowing in the direction indicated by arrow 48 in fig5 is diverted by the windfoil over the top of mailbox 26 , causing eddies 50 to form on the leeward side 52 of pile 20 as shown by flow lines 54 in fig5 . particulate solids entrained in the wind drop out of the air in the area 56 of the eddies onto the leeward side 52 of pile 20 as indicated at 58 in fig5 . that keeps the particulate material from being carried away from the pile . it is important in this respect that windfoil 42 eliminates the venturi effect appurtenant to an unprotected pile as discussed in conjunction with fig4 . consequently , such air as might flow between conveyor 24 and the top 44 of pile 20 will have a much lower velocity and will be less apt to pick up fines from particulate material being dumped onto the pile . in actual practice , it has been found that some of the particulate material will also drop out of the air currents onto the leeward side of mailbox 26 . this material simply slides down the side of the mailbox onto the leeward side of pile 20 . referring now specifically to fig3 the structural framework 30 of conveyor 24 includes a longitudinal beam 60 extending along the midline of pile 20 . the several sections 45 of windfoil 42 , reinforced along their upper edge by a boxlike structure made up of angle irons 62 , are pivotally supported from beam 60 by a pair of axially aligned hinges 64 and 66 . these hinges include a strap 67 fixed to beam 60 and a second strap 68 which is attached to the associated windfoil section 45 and connected to the beam - attached strap 68 by a shear pin 70 . thus pivotally supporting the windfoil 42 from conveyor 24 substantially reduces wind loads on the former . for windfoil 42 to prevent the entrainment of particulate material in the manner described above , the lower edge of that windfoil can be proximate to ( i . e ., spaced slightly above ) or in contact with the top 44 of pile 20 , or that edge of the windfoil can be buried in the particulate material making up the pile . in the latter case , wind loads on the windfoil are partially transferred to and absorbed by the material making up the pile . wind loads on windfoil 42 can also be reduced by appropriately perforating the sections 45 making up the windfoil . such perforations are shown diagramatically in fig3 and identified by reference character 72 . as particulate solids are withdrawn from the bottom of pile 20 in the manner discussed above in conjunction with fig1 downwardly acting forces of considerable magnitude can be imposed upon the windfoil sections 45 by virtue of the friction between them and the particulate solids in the pile . shear pins 70 prevent those downwardly acting forces from reaching a magnitude at which damage to structural components of conveyor 24 might result . the shear pins similarly function to keep unacceptably high wind loads from being imposed on the conveyor . to further minimize the possibility of damage to conveyor 24 by downwardly directed forces , windfoil sections 45 with smooth surfaces are preferably employed in the interest of minimizing the friction between those sections and the particulate material in pile 20 . as suggested above , steel is one suitable material for the windfoil . aluminum and other structural metals can of course also be used . referring again to fig2 windfoil 42 effectively prevents the entrainment of particulate material during dumping and by the erosion of particulate material from pile 20 by winds blowing across or quartering the pile . entrainment of the solids making up the pile by winds blowing in a direction more closely approaching the longitudinal axis of pile 20 can be prevented by suspending a second windfoil 74 from the structural framework of conveyor 24 at the end of windfoil 42 coterminous with the end of pile 20 . windfoil 74 is oriented to extend crosswise of pile 20 and can , like windfoil 42 , be made up from more than one section . also , it will preferably be pivotally suspended from cross beam 75 of conveyor 24 by shear pins as discussed above and shown in fig3 to reduce wind loads on it and to guard against damage to the conveyor &# 39 ; s structural components . as discussed above , and shown in fig5 the formation of eddy currents 50 on the leeward side 52 of pile 20 is an important function of windfoil 42 . the formation of such eddies can in some cases be promoted by disposing transversely oriented intermediate windfoils at intervals along windfoil 42 ( a typical location is indicated by reference 76 ). the intermediate windfoils limit the effective length of the longitudinally extending windfoil 42 , thereby favoring the formation of the eddy currents . these intermediate windfoils are , preferably , also pivotally suspended from cross beams of the structural framework of conveyor 24 with shear pins in the manner shown in fig3 . the invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof . the present embodiments are therefore to be considered in all respects as illustrative and not restrictive , the scope of the invention being indicated by the appended claims rather than by the foregoing description ; and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein .