Cocktail Boothby's American Bar-Tender by Wm. T. Boothby (1891, p.49)

1 jiggervermouth base
Apollinaris mineral water — Apollinarisdilution
gum syrup — Added to taste.sweetener
  1. Place ice, gum syrup to taste, and a jigger of vermouth in a long thin glass.
  2. Fill with Apollinaris, stir, and serve.

Ice: Cube ice

This is a useful low-proof aperitif checkpoint because it treats vermouth as a complete mineral-water service drink, not just a cocktail modifier.

The identity lies in direct in-glass lengthening with mineral water rather than stirring a compact cocktail.

See also: Vermouth Cocktail, Amer Picon

Boothby calls it a great French beverage.