Received the following question in a comment:
“I’m curious about the ‘evidence’ for Hercules being a wine-and-herbal yerba-mate drink. Some years ago I thought I found ‘evidence’ that it was a very strong Welsh beer, ie: there was a brand with that name. Since then I have concluded that Hercules was a British version of absinthe, or possibly Czech absinthe bottled here. Vantogrio was certainly Czech. My guess is that it was a non-alcoholic anise-flavoured syrup. But Hercules just has to be strong…”
While there have undoubtedly been numerous products named Hercules over the years, I believe the evidence is fairly conclusive that the “Hercules” called for in Savoy Cocktails was neither an Absinthe Substitute nor a strong Belgian Beer.
Please refer to the topic on eGullet for the full rundown of the timeline of events and theories.
Here are some of the ads which friends have turned up and scanned from various London publications, contemporaneous with the publication of the Savoy Cocktail Book.
From the Times, 1927:
From vol. 74 of the Strand Magazine, Jul-Dec. 1927:
From Harry’s ABC of Mixing Cocktails, ca. 1928:
From the Times, dated April 21, 1928: