 Rask was also the first to clearly formulate the laws of sound-correspondence in the different languages, especially in the vowels (previously ignored by etymologists).The "Grammar" was continued in three volumes, treating principally derivation, composition and syntax, the last of which was unfinished.Grimm then began a third edition, of which only one part, comprising the vowels, appeared in 1840, his time being afterwards taken up mainly by the dictionary.