Conception. The circumscribed thing is always smaller than that which circumscribes it. If there be 2 surfaces laid one upon the other, such that the one neither exceeds the other nor is exceeded by it, then without doubt they are equal. By the first [proposition], this second is not general, because when the surface of the cylinder is clothed by the water or the air that surrounds it, their surfaces are not equal. The adversary says that the surface of the cylinder and of the water that clothes it are one and the same thing, since the cylinder ends at the boundary of the water and the water has for its boundary the boundary of the cylinder, and between the one boundary and the other nothing is interposed. Here it is answered that the boundary of the cylinder is of the proper substance of that cylinder, and the boundary of the water is of the substance of that water. Therefore this concludes that there are 2 surfaces that circumscribe one another, which, by the first conception, are one greater than the other.