(uh, my French pronounciation is worse than my reading comprehension -- do they not rhyme because of the difference between "te" and "tte," and/or is there some slight difference in the vowel? I suck so badly at vowels!)
Short answer: they rhyme today but didn't necessarily rhyme in Voltaire's day.
Long answer...well, bear in mind that I had only one semester on the history of the French language--selenak, my PhD was in historical linguistics--so the following explanation is derived from Wikipedia plus the 15-year-old hazy memory of a non-French speaker. But Wikipedia matches my memories closely enough that I'm just going to go with it.
Originally, back in Cicero's day in Latin, "t" and "tt" would have been pronounced differently, but by about the year 1000 they were pronounced the same in French. So Voltaire would not have heard any difference between the consonants. It's the vowels he would have cared about.
Now, the word "tête" comes from Latin "testa". Some time in the Middle Ages, "s" before a following consonant got turned to "h", pronounced "tehta".
Then the "h" stopped being pronounced, but to make up for the lost consonant, the preceding vowel went from a short vowel to a long vowel. This was represented by putting a circumflex over the vowel. So "tête" had a long vowel, and "trompette" a short vowel, for several hundred years, and the modern spelling difference reflects this historical difference.
Around Voltaire's time, French speakers stopped pronouncing vowel length differences. Like most sound changes, this took multiple generations and caught on gradually. There was a period when some people were pronouncing them the same, and some people were pronouncing them differently.
My guess (this is an educated guess) is that in ordinary, casual speech in France, and in German-speaking regions, the two words rhymed, but someone known for speaking the "best", i.e. conservative, French, like Voltaire, would still observe a difference, especially because they were spelled differently, and because the poets of preceding generations Voltaire and Fritz were emulating were not rhyming them.
Today, they rhyme in most dialects, including in Paris, and I know this not because I can pronounce French vowels*, but because I asked a friend who grew up just outside Paris to confirm Wikipedia.
* I barely even pronounce English vowels: people make fun of what vowels I rhyme and don't rhyme all the time. :P Case in point, I pronounce "sell" and "sail" the same. I have most but not all the mergers on this page.
French pronunciation
Short answer: they rhyme today but didn't necessarily rhyme in Voltaire's day.
Long answer...well, bear in mind that I had only one semester on the history of the French language--
Originally, back in Cicero's day in Latin, "t" and "tt" would have been pronounced differently, but by about the year 1000 they were pronounced the same in French. So Voltaire would not have heard any difference between the consonants. It's the vowels he would have cared about.
Now, the word "tête" comes from Latin "testa". Some time in the Middle Ages, "s" before a following consonant got turned to "h", pronounced "tehta".
Then the "h" stopped being pronounced, but to make up for the lost consonant, the preceding vowel went from a short vowel to a long vowel. This was represented by putting a circumflex over the vowel. So "tête" had a long vowel, and "trompette" a short vowel, for several hundred years, and the modern spelling difference reflects this historical difference.
Around Voltaire's time, French speakers stopped pronouncing vowel length differences. Like most sound changes, this took multiple generations and caught on gradually. There was a period when some people were pronouncing them the same, and some people were pronouncing them differently.
My guess (this is an educated guess) is that in ordinary, casual speech in France, and in German-speaking regions, the two words rhymed, but someone known for speaking the "best", i.e. conservative, French, like Voltaire, would still observe a difference, especially because they were spelled differently, and because the poets of preceding generations Voltaire and Fritz were emulating were not rhyming them.
Today, they rhyme in most dialects, including in Paris, and I know this not because I can pronounce French vowels*, but because I asked a friend who grew up just outside Paris to confirm Wikipedia.
* I barely even pronounce English vowels: people make fun of what vowels I rhyme and don't rhyme all the time. :P Case in point, I pronounce "sell" and "sail" the same. I have most but not all the mergers on this page.