light is represented as filaments, rays, or as vibrations of the ether, or as globules of ether, each of which strikes on the other. This is an analogy quite in the manner of Epicurus. In giving such explanations as those above, Epicurus professed to be most liberal, fair and tolerant, saying that all the different conceptions which occur to us in relation to sensuous objects—at our pleasure, we may say,—can be referred to that which we cannot ourselves directly observe; we should not assert any one way to be the right one, for many ways may be so. In so saying, Epicurus is talking idly; his words fall on the ear and the fancy, but looked on more narrowly they disappear. So, for instance, we see the moon shine, without being able to have any nearer experience of it. On this subject Epicurus says: “The moon may have its own light, or a light borrowed from the sun; for even on earth we see things which shine of themselves, and many which are illuminated by others. Nothing hinders us from observing heavenly things in the light of various previous experiences, and from adopting hypotheses and explanations in accordance with these. The waxing and waning of the moon may also be caused by the revolution of this body, or through changes in the air” (according as vapour is modified in one way or another), “or also by means of adding and taking away somewhat: in short, in all the ways whereby that which has a certain appearance to us is caused to show such appearance.” Thus there are to be found in Epicurus all these trivialities of friction, concussion, &c., as when he gives his opinion of lightning on the analogy of how we see fire of other kinds kindled: “Lightning is explained by quite a large number of possible conceptions; for instance, that through the friction and collision of clouds the figuration of fire is emitted, and lightning is produced.” In precisely the same way modern physicists transfer the production of an electric spark, when glass and silk are rubbed against each other, to the clouds. For, as we see a spark both in lightning and electricity, we conclude from this circumstance common to both that the two are analogical; therefore, we come to the conclusion that lightning also is an electric phenomenon. But clouds are not hard bodies, and by moisture electricity is more likely to be dispersed; therefore, such talk has just as little truth in it as the fancy of Epicurus. He goes on to say: “Or lightning may also be produced by being expelled from the clouds by means of the airy bodies which form lightning—by being struck out when the clouds are pressed together either by each other or by the wind,” &c. With the Stoics things are not much better. Application of sensuous conceptions according to analogy is often termed comprehension or explanation, but in reality there is in such a process not the faintest approach to thought or comprehension. “One man,” adds Epicurus, “may select; one of these modes, and reject the