In Indo-Hittite long vowels and diphthongs with long prior element were shortened before h. In Pre-Indo-European h was lost in all positions, and an immediately preceding vowel was lengthened if h had been followed by another consonant. These phonetic laws furnish an explanation of certain vowel alternations in Greek and Sanskrit which have hitherto been ascribed with some difficulty to ablaut.
E. H. Sturtevant (Mon,) studied this question.
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