Endnote 22
Part I, §19, l. 7.  cenith, as here used, has a totally different meaning from that of senith, in l. 1 above.  The senith in l. 1 is what we still call the zenith; but the cenith in l. 7 means the point of the horizon denoting the sun's place in azimuth. Contrary to what one might expect, the latter is the true original meaning, as the word zenith is corrupted from the root of the word which we now spell azimuth.  The Arabic as-sant is a way or path; al-samt, a point of the horizon, and, secondly, an azimuthal circle.  The plural of al-samt is assumut, whence azimuth.  But zenith is a corruption of semt, from samt al-ras, the Arabic name of the vertex of heaven (ras meaning a head); and the qualifying al-ras, the most important part of the phrase, has been improperly dropped.  So far from the reading cenith being wrong here, it is most entirely right, and may be found (better spelt cenit) in the same sense in Messahala.  See p. 213, second footnote.  For cenith, some late copies have signet, evidently taken from the Latin word signum.  They make the same mistake even in l. 12 of section 18.