klaxon stentor electric mfg argued decided june john thomas smith new york city james carpenter jersey city petitioner murray bernays new york city respondent justice reed delivered opinion principal question case whether diversity cases federal courts must follow conflict laws rules prevailing sit left open ruhlin new york life insurance company note frequent recurrence problem well conflict approach problem third circuit opinion first circuit sampson channell led us grant certiorari respondent new york corporation transferred entire business petitioner delaware corporation petitioner contracted use best efforts manufacture sale certain patented devices covered agreement respondent share petitioner profits agreement executed new york assets transferred petitioner began performance although later moved operations respondent voluntarily dissolved new york law ten years later instituted action district district delaware alleging petitioner failed perform agreement use best efforts jurisdiction rested diversity citizenship respondent recovered jury verdict upon judgment entered respondent moved correct judgment adding terest rate six percent june date action brought basis motion provision section new york civil practice act directing contract actions interest added principal sum theretofore liquidated unliquidated district granted motion taking view rights parties governed new york law new york law addition interest mandatory circuit appeals affirmed granted certiorari limited question whether section new york civil practice act applicable action federal delaware circuit appeals view new york law right interest verdict section went substance obligation proper construction contract suit fixed new york place performance concluded section applicable case clear think undoubtedly better view law rules ascertaining measure damages matter procedure matters substance settled reference law appropriate state according type case tried forum measure damages breach contract determined law place performance restatement conflict laws referred also section restatement makes interest part damages determined law place performance application new york statute apparently followed independent determination view without regard delaware law delaware decision statute cited discussed opinion prohibition declared erie railroad mpkins independent determinations federal courts extends field conflict laws conflict laws rules applied federal delaware must conform prevailing delaware state courts otherwise accident diversity citizenship constantly disturb equal administration justice coordinate state federal courts sitting side side see erie railroad tompkins supra ruling violence principle uniformity within state upon tompkins decision based whatever lack uniformity may produce federal courts different attributable federal system leaves state within limits permitted constitution right pursue local policies diverging neighbors federal courts thwart local policies enforcing independent law conflict laws subject review federal question may arise delaware free determine whether given matter governed law forum law cf milwaukee county white views decisive factor determining applicable conflicts rule cf funkhouser preston proper function delaware federal ascertain state law besides general considerations traditional treatment interest diversity cases brought federal courts points conclusion section revised statutes relating interest judgments provides calculated date judgment rate allowed law judgments recovered courts state held massachusetts benefit association miles page page held section exclude allowance interest verdicts well judgments opinion observed courts state federal courts sitting within state harmony upon point looking delaware cases petitioner relies one group support contention delaware state courts refuse apply section new york civil practice act respondent another prove contrary make analysis delaware decisions leave circuit appeals case remanded respondent makes argument judgment must affirmed full faith credit clause constitution art state courts delaware obliged give effect new york statute argument rests mainly decision john hancock mutual life insurance company yates new york statute held integral part contract insurance georgia compelled sustain contract full faith credit clause however section new york civil practice act way related validity contract suit merely incidental item damages interest respect courts forum commonly free apply law see fit nothi constitution ensures unlimited extraterritorial recognition statutes statute circumstances pacific employers insurance industrial accident kryger wilson full faith credit clause go far compel delaware apply section application interfere local policy accordingly judgment reversed case remanded circuit appeals decision conformity law delaware reversed remanded footnotes section new york civil practice act included recovery action except provided section four hundred final judgment rendered sum money awarded verdict report decision interest upon total amount awarded time verdict rendered report decision made time entering judgment must computed clerk added total amount awarded included amount judgment every action wherein sum money shall awarded verdict report decision upon cause action enforcement based upon breach performance contract express implied interest shall recovered upon principal sum whether theretofore liquidated unliquidated shall added part total sum awarded opinion sampson channell reaches conclusion opinion third circuit handed subsequent case bar waggaman general finance see also goodrich conflict laws