“ The findings on these special issues do not exhaust all of the possible grounds on which the prior unsafe-place-to-work finding of the jury may have been based. Hence all of the findings in the case might well be true insofar as the record indicates. The petitioner having asserted federal rights governed by federal law, it is our duty under the Act to make certain that they are fully protected, as the Congress intended them to be. ”

“ We therefore cannot accept interpretations that nullify their effectiveness, for '* * * the assertion of Federal rights, when plainly and reasonably made, is not to be defeated under the name of local practice.' Davis v. ”