And therefore my opinion is, not that they are things subsisting by themselves without matter, but that there can no abstraction be made of motion and figure from matter, and that matter and motion being but one thing and inseparable, make but one substance. Wherefore density and rarity, gravity and levity, &c. being nothing else but change of motions, cannot be without matter, but a dense or rare, heavie or light matter is but one substance or body; And thus having obeyed your commands, I rest, Madam, _Your faithful Friend,_ _and Servant._ XLIV. _MADAM,_ I am very ready to give you my opinion of those two questions you sent me, whereof the first was, _Whether that, which is rare and subtil, be not withal pure?_ To which I answer, That all rare bodies are not subtil, nor pure, and that all which is dense is not gross and dull: As for example, Puddle-water, or also clear water, is rarer then Quicksilver, and yet not so subtil and pure as Quicksilver; the like of Gold; for Quicksilver and Gold may be rarified to a transparentness, and yet be so dense, as not to be easily dissolved; and Quicksilver is very subtil and searching, so as to be able to force other bodies to divide as well as it can divide and compose its own parts. Wherefore my opinion is, that the purest and subtilest degree of matter in nature, is that degree of matter which can dilate and contract, compose and divide into any figure by corporeal self-motion. Your second question was, _Why a man's hand cannot break a little hard body, as a little nail, whereas yet it is bigger then the nail?_ I answer, It is not because the hand is softer then the nail, for one hard body will not break suddenly another hard body, and a man may easily break an iron nail with his hand, as I have bin informed; but it is some kind of motion which can easier do it, then another: for I have seen a strong cord wound about both a man's hands, who pulled his hands as hard and strongly asunder as he could, and yet was not able to break it; when as a Youth taking the same cord, and winding it about his hands as the former did, immediately broke it; the cause was, that he did it with another kind of motion or pulling, then the other did, which though he used as much force and strength, as he was able, yet could not break it, when the boy did break it with the greatest ease, and turning onely his hands a little, which shews, that many things may be done by a slight of motion, which otherwise a great strength and force cannot do. This is my answer and opinion concerning your proposed questions; if you have any more, I shall be ready to obey you, as, Madam, _Your faithful Friend_ _and humble Servant._ XLV. _MADAM,_