Ferguson's New Astronomical Instrument marked a return to astronomy following a brief involvement with globe-making. The reason for Ferguson's selling his stock of Senex's globe plates and equipment to Benjamin Martin was given in an advertisement as due to "his indifferent state of health" (Daily Advertiser, 16 July 1757). It appears that Ferguson was not in fact terribly ill and perhaps more likely preferred to return to the field in which he had already excelled, prior to his brief foray into the globe business. The New Astronomical Instrument was a slightly improved version of his Astronomical Rotula of 1742, incoporating the star map; however, on this instrument he chose to omit the position of the Moon's nodes, meaning that the instrument could not be used for predicting eclipses. An example of the New Astronomical Instrument is in the British Library, Map Collection, K.190.