3. Words ending in r, as par, fer, vir, cor, fur. These had that form of long vowel which we use in 'part', 'fertile', 'virtue', 'cordate', 'furtive'.
In, disyllables the former vowel or diphthong, if followed by a single consonant, or by a mute and r, or by cl or pl, was pronounced long, a usage which according to Mr. Henry Bradley dates in spoken Latin from the fourth century. Examples are apex, tenet, item, focus, pupa, Psyche, Cæsar, fœtus. I believe that at first the only exceptions were tibi, sibi, ibi, quibus, tribus. In later days the imperfect and future of sum became exceptions. Here perhaps the short vowel arose from the hideous and wholly erroneous habit, happily never universal though still in some vogue, of reciting erám, erás, erát. There are actually schoolbooks which treat the verse ictus, the beat of the chanter's foot, as a word stress and prescribe terra tribús scopulís. I can say of these books only Pereant ipsi, mutescant scriptores, and do not mind using a post-classical word in order to say it.
In disyllables the former vowel or diphthong, if followed immediately by another vowel or diphthong, had the quality, and if emphatic also the quality, of a long vowel. The distinction was not recognized, and seems not to be generally acknowledged even now. We seem not to have borrowed many words which will illustrate this. We have however fiat, and pius was pronounced exactly as we pronounce 'pious', while for a diphthong we may quote Shelley,
Mid the mountains Euganean
I stood listening to the paean.
English derivatives will show the long quality of the vowels in aer, deus, coit, duo. To these add Graius.
The rule of apex applies also to words of more than two syllables with long penultima, as gravamen, arena, saliva, abdomen, acumen. The rule of aer also holds good though it hardly has other instances than Greek names, as Macháon, Ænéas, Thalía, Achelóus, Achǽi.
In words of more than two syllables with short penultima the vowel in the stressed antepenultima was pronounced short when there was a consonant between the two last vowels, and i and y were short even when no consonant stood in that place. Examples are stamina, Sexagesima, minimum, modicum, tibia, Polybius. But u, au, eu were, as usual, exceptions, as tumulus, Aufidus, Eutychus. I believe that originally men said Cæ̆sarem, as they certainly said cæ̆spitem and Cæ̆tulum, as also Cæ̆sarea, but here in familiar words the cases came to follow the nominative.
Exceptions to the rule were verb forms which had āv, ēv, īv, or ōv in the antepenultima, as amāveram, defieverat, audivero, moveras, and like forms from aorists with the penultima long, as suaseram, egero, miserat, roseras, and their compounds.
This rule was among the first to break down, and about the middle of the nineteenth century the Westminster Play began to observe the true quantities in the antepenultimate syllables. Thus in spite of 'consĭderation' boys said sīdera, and in spite of 'nŏminal' they said nômina, while they still said sŏlitus and răpidus.