Mirrors. If you set a candle between two long mirrors shaped like a roof-tile, in the way here drawn, you will see that by means of these mirrors the candle melts every resistant thing. Question. I wish to understand the weight of a continuous ounce of water falling from the height of one braccio: how much water it can continuously raise to the height of 10 braccia by means of an instrument, and to the height of 20 and of 30, and so on step by step, by way of a general rule.

On resistance. That axle of the cart which is twice as thin as the other will be 4 times easier to turn than the other. And you will see the experiment by holding a bradawl in your hand near the handle, where it will be turned in your hand with difficulty; and if you hold it by the point, whoever holds the handle of that bradawl in his hand will turn it easily between your fingers.

b a. On motion. If you give the motion to the wheels from the end of their counter-levers, you will make a great and weak motion; and if you give that motion from the end of the levers, you will make a great and slow force. a is toward the counter-levers, b is toward the levers. In effect one concludes that, with a single motor, the swifter the force it makes with instruments, the weaker that force will be.

The blow. A blow given in a place that does not resist will be of little effect, as is shown by the difference there is between jumping on the tips of the toes and jumping upon the heels.

The blow. A thing that falls will never deliver a blow suited to its heaviness unless, at the moment of the blow, the whole of it comes to rest upon the blow.

a – d – b – c. Let us say the body d a b weighs 20 pounds and that, descending, it strikes the blow with the part b upon the place c. I say: if b weighs 10 and a 10, it will make a blow of only 10. The reason is that when b has struck, a is still falling, and in falling it does not weigh, at the moment of the blow, upon the struck place. This same thing happens to the man who jumps on the tips of his toes, who at the moment of the impact bends his knees, and all the upper joints behind the blow sink upon the blow, and it makes only as much impact as is the striking part that first comes to rest upon the struck place, that is, from the knee to the foot. Some would say from the heel to the tip of the foot, because in the blow of the tip of the foot the heel sinks somewhat and therefore makes no blow. The blow. The thing that strikes does not make a blow of full effect unless the part that delivers the impact is the centre beneath the falling weight.

b a. When b delivers the impact, a is still falling. A thing that falls will not make a perfect blow unless the place that receives the blow is without motion.