Quaestiones Convivales
Plutarch
Plutarch. Plutarch's Morals, Vol. III. Goodwin, William W., editor; Creech, Thomas, translator. Boston: Little, Brown, and Company; Cambridge: Press of John Wilson and Son, 1874.
But we, according to Plato’s opinion, assert that a bright spirit darted from the eye mixes with the light
about the object, and those two are perfectly blended into one similar body; now these must be joined in due proportion one to another; for one part ought not wholly to prevail on the other, but both, being proportionally and amicably joined, should agree in one third common power. Now this (whether flux, illuminated spirit, or ray) in old men being very weak, there can be no combination, no mixture with the light about the object; but it must be wholly consumed, unless, by removing the letters from their eyes, they lessen the brightness of the light, so that it comes to the sight not too strong or unmixed, but well proportioned and blended with the other. And this explains that common affection of creatures seeing in the dark; for their eye-sight being weak is overcome and darkened by the splendor of the day; because the little light that flows from their eyes cannot be proportionably mixed with the stronger and more numerous beams; but it is proportionable and sufficient for the feeble splendor of the stars, and so can join with it, and co-operate to move the sense.THEON the grammarian, when Metrius Florus gave us an entertainment, asked Themistocles the Stoic, why Chrysippus, though he frequently mentioned some strange phenomena in nature (as that salt fish soaked in salt water grows fresher than before, fleeces of wool are more easily separated by a gentle than a quick and violent force, and men that are fasting eat slower than those who took a breakfast), yet never gave any reason for the appearance. And Themistocles replied, that Chrysippus only proposed such things by the by, as instances to correct us, who easily and without any reason assent to what seems likely,
and disbelieve every thing that seems unlikely at the first sight. But why, sir, are you concerned at this? For if you are speculative and would enquire into the causes of things, you need not want subjects in your own profession; but pray tell me why Homer makes Nausicaa wash in the river rather than the sea, though it was near, and in all likelihood hotter, clearer, and fitter to wash with than that?And Theon replied: Aristotle hath already given an account for this from the grossness of the sea water; for in this an abundance of rough earthy particles is mixed, and those make it salt; and upon this account swimmers or any other weights sink not so much in sea water as in fresh, for the latter, being thin and weak, yields to every pressure and is easily divided, because it is pure and unmixed; and by reason of this subtility of parts it penetrates better than salt water, and so looseneth from the clothes the sticking particles of the spot. And is not this discourse of Aristotle very probable?
Probable indeed, I replied, but not true; for I have observed that with ashes, gravel, or, if these are not to be gotten, with dust itself they usually thicken the water, as if the earthy particles being rough would scour better than fair water, whose thinness makes it weak and ineffectual. Therefore he is mistaken when he says the thickness of the sea water hinders the effect, since the sharpness of the mixed particles very much conduces to make it cleansing; for that opens the pores, and draws out the stain. But since all oily matter is most difficult to be washed out and spots a cloth, and the sea is oily, that is the reason why it doth not scour as well as fresh; and that it is oily, even Aristotle himself asserts, for salt in his opinion hath some oil in it, and therefore makes candles, when sprinkled on them, burn the better and clearer than before. And sea water sprinkled on a flame increaseth it, and is more easily kindled than any other; and this, in my opinion, makes it
hotter than the fresh. Besides, I may urge another cause; for the end of washing is drying, and that seems cleanest which is driest; and the moisture that scours (as hellebore, with the humors that it purges) ought to fly away quickly together with the stain. The sun quickly draws out the fresh water, because it is so light; but the salt water being rough lodges in the pores, and therefore is not easily dried.