These works are lost; but their titles, combined with expressions in the letters of Synesius, who consulted her about the construction of an astrolabe and a hydroscope, indicate that she devoted herself specially to astronomy and mathematics.
Nearly every one of the modern instruments used for the observations of physical astronomy is a part of the perfected astrolabe.
His treatises De mensura astrolabii and De utilitatibus astrolabii (to be found, on the authority of Salzburg MSS., in Pez, Thesaurus anecdotorum novissimus, iii.) being the first contributions of moment furnished by a European to this subject, Hermann was for a time considered the inventor of the astrolabe.
A collection of circles such as is the armillary sphere, if each circle were fitted with a view-tube, might be considered a complete astrolabe.
With the tables of the sun's declination then available, he could calculate his latitude by meridian altitudes of the sun taken with his astrolabe.