It is true that the instances in which we find β taking the place of ου in the first century, and earlier, are decidedly in the minority, but when we recollect that ου was the original and natural representative of the Latin u, the fact that a change was made at all is of great weight, and one instance of β for u would outweigh a dozen instances of the old form, ou. That the letter should be changed in the Greek, even when it had not been in the Latin, seems to make it certain that the ‘Greek ear,’ at least, had detected a real variation of sound from the original u, and one that approached, at least, their β (Eng. v).
Nor, in this connection, should we fail to notice the words in Latin where u consonant is represented by b, such as bubile from bovile, defervi and deferbui from deferveo.
In concluding the argument for the labial v sound of consonantal u, it may be proper to suggest a fact which should have no weight against a conclusive argument on the other side, but which might, perhaps, be allowed to turn the scale nicely balanced. The w sound is not only unfamiliar but nearly, if not quite, impossible, to the lips of any European people except the English, and would therefore of necessity have to be left out of any universally adopted scheme of Latin pronunciation. Professor Ellis pertinently says: “As a matter of practical convenience English speakers should abstain from w in Latin, because no Continental nation can adopt a sound they cannot pronounce.”
X has the same sound as in English.
Marius Victorinus says:
[Keil. t. VI. p. 32.] Dehinc duae supremae s et x jure jungentur, nam vicino inter se sonore attracto sibilant rictu, ita tamen si prioris ictus pone dentes excitatus ad medium lenis agitetur; sequentis autem crasso spiritu hispidum sonet qui per conjunctionem c et s, quarum et locum implet et vim exprimit, ut sensu aurium ducamur efficitur.
Again:
[Id. ib. p. 5.] X autem per c et s possemus scribere.
And:
Posteaquam a Graecis ξ, et a nobis x, recepta est, abiit et illorum et nostra perplexa ratio, et in primis observatio Nigidii, qui in libris suis x littera non est usus, antiquitatem sequens.