▁operating ▁steam ▁engine . ▁ ▁He ▁tried ▁construct ing ▁a ▁model ; ▁it ▁failed ▁to ▁work ▁satisf actor ily , ▁but ▁he ▁continued ▁his ▁experiments ▁and ▁began ▁to ▁read ▁everything ▁he ▁could ▁about ▁the ▁subject . ▁He ▁came ▁to ▁real ise ▁the ▁importance ▁of ▁lat ent ▁heat — the ▁thermal ▁energy ▁released ▁or ▁absor bed ▁during ▁a ▁constant - temper ature ▁process — in ▁understanding ▁the ▁engine , ▁which , ▁unknown ▁to ▁W att , ▁his ▁friend ▁Joseph ▁Black ▁had ▁previously ▁discovered ▁some ▁years ▁before . ▁Under standing ▁of ▁the ▁steam ▁engine ▁was ▁in ▁a ▁very ▁primitive ▁state , ▁for ▁the ▁science ▁of ▁therm od ynam ics ▁would ▁not ▁be ▁formal ised ▁for ▁nearly ▁another ▁ 1 0 0 ▁years . ▁ ▁In ▁ 1 7 6 3 , ▁W att ▁was ▁asked ▁to ▁repair ▁a ▁model ▁New com en ▁engine ▁belonging ▁to ▁the ▁university . ▁Even ▁after ▁repair , ▁the ▁engine ▁bare ly ▁worked . ▁After ▁much ▁experiment ation , ▁W att ▁demonstrated ▁that ▁about ▁three - quarters ▁of ▁the ▁thermal ▁energy ▁of ▁the ▁steam ▁was ▁being ▁consum ed ▁in ▁he ating ▁the ▁engine ▁cyl inder ▁on ▁every ▁cycle . ▁This ▁energy ▁was ▁was ted ▁because ▁later ▁in ▁the ▁cycle ▁cold ▁water ▁was ▁inject ed ▁into ▁the ▁cyl inder ▁to ▁con den se ▁the ▁steam ▁to ▁reduce ▁its ▁pressure . ▁Thus ▁by ▁repeatedly ▁he ating ▁and ▁cool ing ▁the ▁cyl inder , ▁the ▁engine ▁was ted ▁most ▁of ▁its ▁thermal ▁energy ▁rather ▁than ▁converting ▁it ▁into ▁mechanical ▁energy . ▁ ▁W att