Passage 8.38.4
ἢν δὲ αὐχμὸς χρόνον ἐπέχῃ πολὺν καὶ ἤδη σφίσι τὰ σπέρματα ἐν τῇ γῇ καὶ τὰ δένδρα αὐαίνηται, τηνικαῦτα ὁ ἱερεὺς τοῦ Λυκαίου Διὸς προσευξάμενος ἐς τὸ ὕδωρ καὶ θύσας ὁπόσα ἐστὶν αὐτῷ νόμος, καθίησι δρυὸς κλάδον ἐπιπολῆς καὶ οὐκ ἐς βάθος τῆς πηγῆς· ἀνακινηθέντος δὲ τοῦ ὕδατος ἄνεισιν ἀχλὺς ἐοικυῖα ὁμίχλῃ, διαλιποῦσα δὲ ὀλίγον γίνεται νέφος ἡ ἀχλὺς καὶ ἐς αὑτὴν ἄλλα ἐπαγομένη τῶν νεφῶν ὑετὸν τοῖς Ἀρκάσιν ἐς τὴν γῆν κατιέναι ποιεῖ.
If drought persists for a long time, when their crops and trees begin already to wither in the ground, the priest of Zeus Lycaeus prays to the water, performs the sacrifices appointed by custom, and then lowers an oak branch upon the surface—not into the depths—of the spring. Once the water has been stirred, a vapor resembling a mist rises up; after lingering a short while, this mist becomes a cloud and, drawing other clouds toward itself, causes rain to fall upon the land of the Arcadians.