235. Directions have heretofore been given (93) for writing Con-current-Vowels, both between stems and otherwise, with their regular dot and dash signs ; and it may be added that it is entirely proper to always write them with those signs. There are, however, certain groups of vowels, of quite frequent occurrence, in which one element is always the short vowel ĭ, for which special signs are provided, each of which represents a single group; hence they are called " Plural-Vowel Signs." A simple vowel is a sound produced while the vocal organs are held in a fixed or nearly fixed position. A diphthong is a sound made while the vocal organs are passing from one position to another, and is, therefore, changing throughout its entire length. A diphthong, like a simple vowel, is always sounded in one syllable; while a double-vowel is always divided into two syllables. The Two-Vowel Signs are composed of two ticks or breves, joined so as to form acute angles, similar to the signs of the diphthongs, I, OI, and EW, as shown in the table on page 84. It will aid in learning these signs to note that signs that represent all dot-vowel sounds open either upward or downward (see first line of table); and signs which stand for groups, one element of which is a dash-vowel, open either rightward or leftward (see second line of table). As will be observed, the three diphthongs just mentioned fall naturally into appropriate places in this scheme of double-vowel representation. But, as the other diphthong, OW, is a glide-sound from ŏ to 6b, it lies outside of the scheme ; therefore, the author devised for it another form of sign.