Wash, stem, but do not pit, 3 pounds sour cherries.
Crush in saucepan, add 1 cup water (just enough to prevent burning), and simmer until soft.
Strain through jelly bag to measure 3 cups, adding water if necessary.
Place juice in a saucepan, stir in the pectin, making sure there are no lumps, and heat to a hard boil.
Add sugar; stir until dissolved.
Bring to a full rolling boil (a tumbling boil that cannot be stirred down), and boil for 1 minute.
Remove from heat, skim and pour quickly into 6 or 8 hot sterilized jelly glasses.
Cover with paraffin.