Thesameistrueofaloadedgun。Fromthedialecticalstandpoint，thepossibilityofexpressingmotioninitsopposite，inrest，presentsabsolutelynodifficulty。Fromthedialecticalstandpointthewholeantithesis，aswehaveseen，isonlyrelative;thereisnosuchthingasabsoluterest，unconditionalequilibrium。Eachseparatemovementstrivestowardsequilibrium，andthemotionasawholeputsanendagaintotheequilibrium。Whenthereforerestandequilibriumoccurtheyaretheresultoflimitedmotion，anditisself-evidentthatthismotionismeasurablebyitsresult，canbeexpressedinit，andcanberestoredoutofitagaininoneformoranother。ButHerrDühringcannotallowhimselftobesatisfiedwithsuchasimplepresentationofthematter。Asagoodmetaphysicianhefirsttearsopen，betweenmotionandequilibrium，ayawninggulfwhichdoesnotexistinrealityandisthensurprisedthathecannotfindanybridgeacrossthisself-fabricatedgulf。HemightjustaswellmounthismetaphysicalRosinanteandchasetheKantian“thing-in-itself“;foritisthatandnothingelsewhichinthelastanalysisishidingbehindthisundiscoverablebridge。
Butwhataboutthemechanicaltheoryofheatandthetied-uporlatentheatwhich“hasremainedastumbling-block“forthistheory？
If，undernormalatmosphericpressure，apoundoficeatthetemperatureofthefreezingpointistransformedbyheatintoapoundofwaterofthesametemperature，aquantityofheatdisappearswhichwouldbesufficienttowarmthesamepoundofwaterfrom0°to79。4°C，ortoraisethetemperatureof79。4poundsofwaterbyonedegree。Ifthispoundofwaterisheatedtoboilingpoint，thatis，to100°C，andisthentransformedintosteamof100°C，theamountofheatthatdisappears，bythetimethelastofthewaterhaschangedintosteam，isalmostseventimesgreater，sufficienttoraisethetemperatureof537。2poundsofwaterbyonedegree。
Theheatthatdisappearsiscalledtied-up。If，bycooling，thesteamisagaintransformedintowater，andthewater，initsturn，intoice，thesamequantityofheataswaspreviouslytiedupisnowagainsetfree，i。e。，canbefeltandmeasuredasheat。Thissettingfreeofheatonthecondensationofsteamandthefreezingofwateristhereasonwhysteam，whencooledto100°，isonlygraduallytransformedintowater，andwhyamassofwateroffreezingpointtemperatureisonlyverygraduallytransformedintoice。Thesearethefacts。Thequestionis，whathappenstotheheatwhileitistiedup？
Themechanicaltheoryofheat，accordingtowhichheatconsistsinagreaterorlesservibration，dependingonthetemperatureandstateofaggregation，ofthesmallestphysicallyactiveparticlesmolecules