cobblestones The Russian word [bulyzhnik] is closely related to English "ballast" "gravel, broken stone, slag" See OED I, 908. Also related to French and English "boulevard."
air "Ancient Indian grammarians speak of the soul apprehending things with the intellect and inspiring the mind with desire to speak." The New Encyclopædia Britannica 15th Ed. (1985), XXII on" Language," (567).
geologists Müller, Lectures, frequently uses 'geologists' as an example of the natural sciences and compares their work to that of the philologer.
Indo-European languages The classification of languages that follows is based on Meillet 30 ff.. except that Bely combines the Italic and Celtic groups into one, thereby having seven categories as opposed to Meillet's eight.
plosives also called a "stop." A consonant formed by a complete closure of the lips, then released followed by burst of air: p, b, t, d, k, g.
spirants also called "fricatives." These sounds are created when the passage of air through the larynx and then out through the lips is impeded or restricted but not the passage is not completely closed: f, v, s, z, sh, ch, zh, kh.
sonants are voiced speech sounds, and can also describe syllabic consonants: u, w, l, r, m, n. Bely includes the semi-vowels u and w in this group.
Modern linguistics normally distinguishes between "obstruents" (stops, affricates and fricatives) and "sonorants" (nasals, liquids and semi-vowels). Meillet himself categorizes the sounds as "occlusives," "sifflantes," voyelles," and "sonantes." Cf. 53 ff..
A. Meillet Introduction a l'étude comparative des langues indo-européennes Paris 1903.I have not seen the Russian translation of the text.