Herodotus, 10.38 (Hicks)
Next, we must by all means stick to our sensations, that is, simply to the present impressions whether of the mind or of any criterion whatever, and similarly to our actual feelings, in order that we may have the means of determining that which needs confirmation and that which is obscure.
"Ἔτι τε44 τὰς αἰσθήσεις δεῖ πάντως τηρεῖν καὶ ἁπλῶς τὰς παρούσας ἐπιβολὰς εἴτε διανοίας εἴθ᾽ ὅτου δήποτε τῶν κριτηρίων, ὁμοίως δὲ καὶ τὰ ὑπάρχοντα παθη, ὅπως ἂν καὶ τὸ προσμένον καὶ τὸ ἄδηλον ἔχωμεν οἷς σημειωσόμεθα.
I can't confirm the Greek, but, for example, it seems important in this passage that the phrasing would be "perceptIBLE" (able to be perceived) rather than "that which has already been perceived.
That passage doesn't seem to do what you want. I read it as:
τὰς παρούσας ἐπιβολὰς "the present impressions"
παρούσας is "of things, to be by, i.e. ready or at hand; to be present in or at." These are the impressions of the mind being experienced. So, it seems to me to be neither "perceptIBLE" (able to be perceived)" nor "that which has already been perceived" but what is present at the moment, at least in this particular passage.
τὰ ὑπάρχοντα παθη (ta hyparkhonta pathē) "the actual feelings"
ὑπάρχοντα is "to be already in existence; to be laid down, to be taken for granted." We need to take our feelings - pathē - of pleasure/pain into account.
This passage says to me we need to use what we have experienced or are experiencing to determine the nature of that which needs additional evidence or that which is unseen or not evident to the senses.