<s id="A18-3.01.01">1 In the preceding book we have talked about the five powers and have explained the causes by which big loads can be moved by means of small forces, and have dealt with it, in our opinion, in greater detail than our predecessors; </s>
<s id="A18-3.01.02">we also have explained the reason why there is a delay in tools of great force and have treated other things clearly, which are for students, where inclination and pressure are concerned, of great benefit, things that the students can be contented with.</s>
<s id="A18-3.01.03">In this book we are going to describe machines that are useful to facilitate that of which the existence and the application has already been shown and that are also beneficial in the moving of heavy bodies.</s>
<s id="A18-3.01.04">Furthermore we are going to construct tools through which we have benefits in pressing, because these too require a great force in their use.</s>
<s id="A18-3.01.05">Loads that are pulled on the ground are done so on "toads".</s>
<s id="A18-3.01.06">The "toad" is a solid body that is made from a square [piece of] wood whose ends are rounded off.</s>
<s id="A18-3.01.07">Onto these toads one puts the loads and attaches to their ends ropes or anything else that serves for pulling, with which one moves the toads.</s>
<s id="A18-3.01.08">These ropes are either pulled with the hands or with other tools.</s>
<s id="A18-3.01.09">If now the ropes are tightened, the toads glide on the ground.Underneath the toads one attaches thin [pieces of] wood or boards so the toads move on them.</s>
<s id="A18-3.01.10">If the load is light one has to use round [pieces of] wood, if it is, however, heavy, boards, because these cannot be moved quickly.</s>
<s id="A18-3.01.11">For if the rollers roll under the load, they will be crushed under it, because of the strong speed of their motion.</s>
<s id="A18-3.01.12">Some people use neither boards nor rollers, but attach to the ends of the toads hard pulleys, on which they move.</s>
