[Sidenote: The first organ of feeling; and how we came to the knowledge of such objects as are common to the touch and to other senses.] 18. By the _touch_, we feel what bodies are cold or hot, though they be distant from us. Others, as hard, soft, rough, and smooth, we cannot feel unless they be contiguous. The organ of touch is every one of those membranes, which being continued from the _pia mater_ are so diffused throughout the whole body, as that no part of it can be pressed, but the _pia mater_ is pressed together with it. Whatsoever therefore presseth it, is felt as hard or soft, that is to say, as more or less hard. And as for the sense of rough, it is nothing else but innumerable perceptions of hard and hard succeeding one another by short intervals both of time and place. For we take notice of rough and smooth, as also of magnitude and figure, not only by the touch, but also by memory. For though some things are touched in one point, yet rough and smooth, like quantity and figure, are not perceived but by the flux of a point, that is to say, we have no sense of them without time; and we can have no sense of time without memory. ------- CHAPTER XXX. OF GRAVITY. 1. A thick body doth not contain more matter, unless also more place, than a thin.—2. That the descent of heavy bodies proceeds not from their own appetite, but from some power of the earth.—3. The difference of gravities proceedeth from the difference of the impetus with which the elements, whereof heavy bodies are made, do fall upon the earth.—4. The cause of the descent of heavy bodies.—5. In what proportion the descent of heavy bodies is accelerated.—6. Why those that dive do not, when they are under water, feel the weight of the water above them.—7. The weight of a body that floateth, is equal to the weight of so much water as would fill the space, which the immersed part of the body takes up within the water.—8. If a body be lighter than water, then how big soever that body be, it may float upon any quantity of water, how little soever.—9. How water may be lifted up and forced out of a vessel by air.—10. Why a bladder is heavier when blown full of air, than when it is empty.—11. The cause of the ejection upwards of heavy bodies from a wind-gun.—12. The cause of the ascent of water in a weather-glass.—13. The cause of motion upwards in living creatures.—14. That there is in nature a kind of body heavier than air, which nevertheless is not by sense distinguishable from it.—15. Of the cause of magnetical virtue. [Sidenote: A thick body doth not contain more matter, unless also more place, than a thin.]