<p>In early modern physics, the luminiferous aether (or ether) was believed to be an invisible space-filling substance or field that was a transmission medium for electromagnetic or gravitational forces.</p>
<p>Peter Guthrie Tait (1837-1901) was a Scottish mathematical physicist, whose investigations in knot theory contributed to the field of topology as a mathematical discipline. His tabulations of knots with ten crossings, which became known as the <em>Tait conjectures</em>, arose out of experiements he conducted with William Thomspon (Lord Kelvin) in 1867 at the University of Edinburgh.</p>
<p>The unknot, or <i>torus</i>, is the first type of mathematical knot listed in knot theory. Intuitively, the unknot is a closed loop of rope without a knot in it.</p>
<p>Mathematical knots, or knots which are studied in the field of knot theory, are based on the embedding of a circle within three-dimensional space. They are different from the usual idea of a knot, that is, a string with free ends. Therefore, mathematical knots are (almost) always considered to be closed loops.</p>