1692–1717, Robert South, Twelve Sermons Preached upon Several Occasions, volumes (please specify |volume=I to VI), London:
The foregoing doctrine affords us also a touchstone for the trial of spirits.
1950 January, Cecil J. Allen, “British Locomotive Practice and Performance”, in Railway Magazine, page 12:
"Expectation of life" is an elastic term: the touchstone here is rather the aggregate amount of work that the locomotive does during its working life.
2002 January, Eve Garrard, “Forgiveness and the Holocaust”, in Ethical Theory and Moral Practice, page 147:
Although there has not been very much direct treatment of the Holocaust in analytic moral philosophy, the Nazis appear again and again as examples or touchstones in the construction of moral theories.
2012, Ann Baynes Coiro, Thomas Fulton, Rethinking Historicism from Shakespeare to Milton, page 243:
In the print firestorm that followed the publication of the royal couple's letters, the generalissima was one polemical touchstone. The Annotations to The Kings Cabinet Opened itself depicted the queen as an enemy to king and country: […]
