of astronomers William Wales and William Bayly who were assessing their suitability for measuring longitude. During this period, Arnold also made at least one precision pocket watch, a miniature version of the larger marine timekeepers. This surviving watch dates from around 1769–1770, and is signed Arnold No. 1 Invenit et Fecit (Latin for 'invented and made'). The movement, which indicates centre seconds, has a steel balance with a bimetallic temperature compensation strip that acts on the flat balance spring. Though now altered, the original escapement was Arnold's horizontal pivoted detent as fitted to the larger timekeepers, which was, it seems, not entirely successful and needed improvements. Around 1772, Arnold modified this escapement so that it now was pivoted vertically and acted on by a spring. This was a much more successful arrangement, and it is known that in 1772 at least two pocket timekeepers with this escapement were supplied to Joseph Banks at a cost of £100 (Arnold No.5), and also Banks' fellow Etonian Captain Constantine John Phipps, 2nd Baron Mulgrave. In a long and detailed article on this matter published in Australiana November 2014 Vol 36 No. 4, John Hawkins details the association between these two men and the imagined possibility that this instrument is one and the same. The world's first pocket chronometer originally destined for Cook's second voyage, purchased by Banks and lent to Phipps is known to have been a small centre seconds watch of a similar kind to those made by Ellicott. In 1773, Captain Phipps made a voyage to the North Pole, taking with him not only his Arnold pocket timekeeper and an Arnold box timekeeper in gimbals, but also Kendall's "K2" timekeeper. From Phipps's account, it appears that the pocket watch performed very well indeed and was a convenient instrument for ascertaining the longitude. It seems likely that before 1775, Arnold's earliest pocket chronometers, such as those supplied to Phipps and Banks, were plain watches with centre seconds motion, largely resembling Maskelyne's cylinder watch by Ellicott. Certainly, those few surviving examples are of this caliper such as No. 3. By 1772, Arnold had finalized the design of his pocket timekeepers and started series production with a standardized movement caliper, this being around 50 mm in diameter, larger than a conventional watch of the period, and showing seconds with a pivoted detent escapement and spiral compensation curb. However, the latter appears to have proved