The second or autumnal summer, said to last thirty days, begins about the time that the sun enters Scorpio (October 23rd). It is variously called -
(1) St. Martin's summer (L'éte de St. Martin). St. Martin's Day is the 11th November.
“Expect St. Martin's summer, halcyon days.”
(2) All Saints' summer (All Saints' is the 1st November), or All Hallowen summer.
Then followed that beautiful season, Called by the pious Arcadian peasants the summer of All Saints.
“Farewell. All Hallowen summer.” —
(3) St. Luke's little summer (St. Luke's day is 18th October).
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894