Choose well-ripened, good, sound quinces; peel, cut in four, and immerse them in a basin of water. Cover the basin, place it on the fire, and cook the quinces thoroughly, then pour them on a sieve to drain off the juice, collecting it in a bowl. Filter this juice through a flannel bag, return it to the bowl, add the same weight of sugar, cook and finish the same as apple jelly.
Ranhofer assumes you have already read his apple jelly entry, so the finishing instructions are missing here. What follows fills the gaps and gives the numbers he leaves out.
Quince is one of the oldest jelly fruits in Europe, and the word marmalade descends from marmelo, the Portuguese for quince, long before it attached itself to oranges. The fruit is hard, sour and astringent raw, but it is exceptionally high in both pectin and acid, which is precisely the pair a jelly needs, so cooks who had no commercial pectin relied on it heavily. Charles Ranhofer, chef at Delmonico's in New York and author of The Epicurean (1894), gives it in the French idiom he worked in. Quinces were common in American kitchen gardens in the nineteenth century and largely disappeared from them in the twentieth, which is why a recipe that once needed no explanation now does.