Yep, that´s right! The full recipe is (according to my reprint-copy with the black-dressed-couple on the cover):

"Use a 10-ounce glass.
Cracked Ice.
1/3 Creme Cassis.
2/3 Nolly Prat Vermouth.
Sparkling water.
Stir with a spoon and serve."

Have a nice week! :-)