motion is either something or nothing, body or no body, substance or no substance; if nothing, it cannot enter into another body; if something, it must lessen the bulk of the body it quits, and increase the bulk of the body it enters, and so the Sun and Fire with giving light and heat, would become less, for they cannot both give and keep at once, for this is as impossible, as for a man to give to another creature his human Nature, and yet to keep it still. Wherefore my opinion is for heat, that when many men stand round about a fire, and are heated and warmed by it, the fire doth not give them any thing, nor do they receive something from the fire, but the sensitive motions in their bodies pattern out the object of the fires heat, and so they become more or less hot according as their patterns are numerous or perfect; And as for air, it patterns out the light of the Sun, and the sensitive motions in the eyes of animals pattern out the light in the air. The like for Ecchoes, or any other sound, and for the figures which are presented in a Looking-glass. And thus millions of parts or creatures may make patterns of one or more objects, and the objects neither give nor loose any thing. And this I repeat here, that my meaning of Perception may be the better understood, which is the desire of, Madam, _Your faithful Friend,_ _and Servant._ XXV. _MADAM_ I perceive you are not fully satisfied with my former Letter concerning Eccho, and a figure presented in a Looking-glass; for you say, how is it possible, if Eccho consists in the ears patterning out of a voice or sound, but that it will make a confusion in all the parts of the air? My answer is, that I doe not say that Eccho is onely made by the patterning out of the voice or sound, but by repeating the same voice or sound, which repetition is named an Eccho, for millions of ears in animals may pattern out a voice or words, and yet never repeat them, and so may millions of parts of the air; wherefore Eccho doth not consist in the bare patterning out, but in the repetition of the same sound or words, which are pattern'd out; and so some parts of the air may at one and the same time pattern out a sound and not repeat it, and some may both pattern out, and repeat it, but some may neither pattern out, nor repeat it, and therefore the Repetition, not the bare Patterning out is called Eccho: Just as when two or more men do answer or mock each other, and repeat each others words, it is not necessary, if there were a thousand standers by, that they should all do the same. And as for the figure presented in a Looking-glass, I cannot conceive it to be made by pressure and reaction; for although there is both pressure and reaction in nature, and those very frequent amongst natures Parts, yet they do neither make perception nor production, although both pressure and reaction are made by corporeal self-motions; Wherefore the figure presented in a Looking-glass, or