John Calvin, Institutes III.xx.12, trans. Ford Lewis Battles (Library of Christian classics 21 (Philadelphia: The Westminster Press, 1960), 865); COS IV, p. 311 l. 38 ff. ("preces in aerem frustra proiici, nisi spes sit annexa, unde velut e specula Deum quieti expectemus").
There is a lovely little play on words here. For specula, -ae (fem.) is two different words in Latin, really:
- from the verb specio: a look-out, watchtower.
- diminutive of spes, which is related to the verb spero (the 1st edition of the Oxford Latin dictionary, though, says spatium): a little hope, ray of hope.
Moreover, specto, on which ex(s)pecto (cf. expectemus, "we . . . watch") is built, is itself related to specio, being a frequentative of it: specio, to look at, behold; specto, to look at carefully, contemplate, observe, watch.