Notes on Prosody

The book Notes on Prosody by polyglot author Vladimir Nabokov compares differences in iambic verse in the English and Russian languages, and highlights the effect of relative word length in the two languages on rhythm. Nabokov also proposes an approach for scanning patterns of accent which interact with syllabic stress in iambic verse. Originally Appendix 2 to his Commentary accompanying his translation of Aleksandr Pushkin's "Eugene Onegin", "Notes on Prosody" was released separately in book form.
"Notes on Prosody" and Nabokov's translation of "Eugene Onegin" sparked considerable academic debate.
Bely's influence.
Nabokov in large part follows the system described by Andrei Bely in his paper "Description of the Russian iambic tetrameter" ("Опыт характеристики русского четырехстопного ямба") published in the collection of essays "Symbolism" ("Символизм") (Moscow, 1910).
Terminology.
The word stress is reserved for the underlying unvarying pattern of the iambic rhythm, and the word accent is used to describe where the accent falls in speaking a line.
He introduces the notion of a scud, which he defines to be an unaccented stress (page 9). He uses U shaped symbol and / to illustrate. 
He describes a number of types of scuds (page 18):
Differences between Russian and English verse.
The primary source of the differences between Russian and English verse is that English has many one syllable nouns, verbs, and adjectives, where Russian words typically have many syllables, and carry only a single invariable stress. The iambic rhythm of alternating accented and unaccented syllables is relatively natural in English, whereas in Russian speech many unaccented syllables may quite naturally occur in sequence.