Journeyman clocks were first conceived in the early 1760's and the first known reference to one is mentioned in a paper written by Nevil Maskelyne, the future Astronomer Royal, for the the Philosophical Transactions, vol. LIV, p.573, 1761 whilst on the island of St. Helena soon after the Transit of Venus. In it he writes ...I still continued for some time to make my observations in the upper room, as before. For this purpose I fixed up a little clock there which may be called a journeyman or secondary clock having a pendulum swinging seconds which after being well adjusted would keep time very regularly for several hours. It had only a minute and second hand and struck every minute as the second hand came to sixty, which was very convenient for the counting of seconds, more especially in the observations made with the parallactic telescope, it being improper, on account of the instability of the floor, to get up from one's seat or to alter the position of the body considerably even to catch the second, till these observations were completed.
The journeyman clock was also useful for nocturnal observations and so useful were they that on the subsequent voyages for the observation of the Transit of Venus there was sent at least one journeyman (or alarm or assistant clock as they were sometimes refered to) to accompanied them. Two are listed as having been bought from John Shelton and one from Johnathon Monk
These clocks are exceptionally rare and perhaps less than five survive to this day, one of them being in the Meterological office in Lerwick and the other in the National Maritime Museum at Greenwich. The present example has now been altered to strike the hours but it still provides a rare insight into the methods used in the formative years of English astronomy