Theprofitsofstockvarywiththepriceofthecommoditiesinwhichitisemployed。Asthepriceofanycommodityrisesabovetheordinaryoraveragerate，theprofitsofatleastsomepartofthestockthatisemployedinbringingittomarket，riseabovetheirproperlevel，andasitfallstheysinkbelowit。Allcommoditiesaremoreorlessliabletovariationsofprice，butsomearemuchmoresothanothers。Inallcommoditieswhichareproducedbyhumanindustry，thequantityofindustryannuallyemployedisnecessarilyregulatedbytheannualdemand，insuchamannerthattheaverageannualproducemay，asnearlyaspossible，beequaltotheaverageannualconsumption。Insomeemployments，ithasalreadybeenobserved，thesamequantityofindustrywillalwaysproducethesame，orverynearlythesamequantityofcommodities。Inthelinenorwoollenmanufactures，forexample，thesamenumberofhandswillannuallyworkupverynearlythesamequantityoflinenandwoollencloth。Thevariationsinthemarketpriceofsuchcommodities，therefore，canariseonlyfromsomeaccidentalvariationinthedemand。A
publicmourningraisesthepriceofblackcloth。Butasthedemandformostsortsofplainlinenandwoollenclothisprettyuniform，soislikewisetheprice。Butthereareotheremploymentsinwhichthesamequantityofindustrywillnotalwaysproducethesamequantityofcommodities。Thesamequantityofindustry，forexample，will，indifferentyears，produceverydifferentquantitiesofcorn，wine，hops，sugar，tobacco，etc。Thepriceofsuchcommodities，therefore，variesnotonlywiththevariationsofdemand，butwiththemuchgreaterandmorefrequentvariationsofquantity，andisconsequentlyextremelyfluctuating。Buttheprofitofsomeofthedealersmustnecessarilyfluctuatewiththepriceofthecommodities。Theoperationsofthespeculativemerchantareprincipallyemployedaboutsuchcommodities。Heendeavourstobuythemupwhenheforeseesthattheirpriceislikelytorise，andtosellthemwhenitislikelytofall。
Thirdly，thisequalityinthewholeoftheadvantagesanddisadvantagesofthedifferentemploymentsoflabourandstockcantakeonlyinsuchasarethesoleorprincipalemploymentsofthosewhooccupythem。
Whenapersonderiveshissubsistencefromoneemployment，whichdoesnotoccupythegreaterpartofhistime，intheintervalsofhisleisureheisoftenwillingtoworkasanotherforlesswagesthanwouldotherwisesuitthenatureoftheemployment。
TherestillsubsistsinmanypartsofScotlandasetofpeoplecalledCottersorCottagers，thoughtheyweremorefrequentsomeyearsagothantheyarenow。Theyareasortofoutservantsofthelandlordsandfarmers。Theusualrewardwhichtheyreceivefromtheirmastersisahouse，asmallgardenforpot—herbs，asmuchgrassaswillfeedacow，and，perhaps，anacreortwoofbadarableland。Whentheirmasterhasoccasionfortheirlabour，hegivesthem，besides，twopecksofoatmealaweek，worthaboutsixteenpencesterling。Duringagreatpartoftheyearhehaslittleornooccasionfortheirlabour，andthecultivationoftheirownlittlepossessionisnotsufficienttooccupythetimewhichisleftattheirowndisposal。Whensuchoccupiersweremorenumerousthantheyareatpresent，theyaresaidtohavebeenwillingtogivetheirsparetimeforaverysmallrecompensetoanybody，andtohavewroughtforlesswagesthanotherlabourers。InancienttimestheyseemtohavebeencommonalloverEurope。Incountriesillcultivatedandworseinhabited，thegreaterpartoflandlordsandfarmerscouldnototherwiseprovidethemselveswiththeextraordinarynumberofhandswhichcountrylabourrequiresatcertainseason。Thedailyorweeklyrecompensewhichsuchlabourersoccasionallyreceivedfromtheirmasterswasevidentlynotthewholepriceoftheirlabour。Theirsmalltenementmadeaconsiderablepartofit。Thisdailyorweeklyrecompense，however，seemstohavebeenconsideredasthewholeofit，bymanywriterswhohavecollectedthepricesoflabourandprovisionsinancienttimes，andwhohavetakenpleasuresinrepresentingbothaswonderfullylow。