<s id="A18-2.18.01">18 If now a wheel with cogs meshes with the groove of a screw, then the screw moves, with each rotation it makes, one cog of the wheel further. This we are going to demonstrate in the following way.</s>
<s id="A18-2.18.02">Let us imagine a screw, let it be the screw <ab> and let its screw grooves be <aq>, <de>, <zg> and let each single one of these threads be single.</s>
<s id="A18-2.18.03">Let us now imagine a wheel with cogs put to it, namely <hgeq> and let its teeth <hd>, <ge>, <eq> be fitting to mesh with the screw grooves.</s>
<s id="A18-2.18.04">Let the cog <ge> mesh completely with a screw groove, then the remaining cogs will not mesh with the other screw grooves.</s>
<s id="A18-2.18.05">If we now turn the screw until the point <e> is brought to the position of <g>, then <e> falls on <g>.</s>
<s id="A18-2.18.06">If thus the screw makes one rotation and the cog <ge> comes to the position of cog <gh>, the cog <eq> to the position of cog <ge>, and the cog <eq> now takes the position of <ge>, then, in the rotation that the screw makes, the entire space of the cog shifts.</s>
<s id="A18-2.18.07">In the same manner we have to imagine the procedure with the other cogs.</s>
<s id="A18-2.18.08">Thus as many cogs as there are on the wheel, as many rotations the screw makes, until the wheel has made one rotation.</s>
