Francisco Rodríguez Marín studies «La x de Quixote» in an appendix to his «nueva edición crítica» (Madrid: Atlas, 1947-49), and John Jay Allen comments on this question in the introduction to his edition, Letras Hispánicas, 100-01 (Madrid: Cátedra, 1977), I, 28-29. The valuable information offered by Miguel Romera-Navarro, Autógrafos cervantinos, University of Texas Hispanic Studies, 4 (Austin: University of Texas, 1954), has not been given sufficient attention.
De la pronunciación medieval a la moderna en español, ultimado y dispuesto pana la imprenta por Rafael Lapesa, I (Madrid: Credos, 1955), p. 15.
The standard work on the topic is Felipe Robles Dégano, Ortología clásica de la lengua castellana (Madrid: Tabarés, 1905).
I believe that this word is correctly accented as an agudo, with the Arabic -í ending, frequently found in Cervantes (borceguí, maravedí, etc.), and not the Italian or Catalan -i, found only rarely. [See «Daniel Eisenberg Corrects», Cervantes 3.2 (1983): 160. -FJ]
Política de Dios, govierno de Christo (Madrid: Castalia, 1966), p. 20. This is the most rigorous edition of any seventeenth-century Spanish text from a printed source; it was reviewed favorably by E. M. Wilson, HR, 37 (1969), 420-23.
Mendele Treip, Milton's Punctuation and Changing English Usage, 1582-1676 (London: Methuen, 1970).
Percy Simpson, Shakespearian Punctuation (Oxford: Clarendon Press, 1911); A. C. Partridge, Orthography in Shakespeare and Elizabethan Drama (Lincoln: University of Nebraska Press, 1964).
Introducing Shakespeare (New York: Penguin, 1947), pp. 32 and 36.
Clásicos Castalia, 77-79 (Madrid: Castalia, 1973). Other editions I will refer to briefly are those of Juan Bautista Avalle-Arce (Madrid: Alhambra, 1979), Martín de Riquer, 3rd edition (Barcelona: Planeta, 1968) -this edition replaces Riquer's older Juventud edition; see Allen, I, 31-, and Rudolph Schevill and Adolfo Bonilla (Madrid, 1928-41).
This passage is found on pp. 258-59 of Volume III of my edition (Madrid: Espasa-Calpe, 1975).